Mobile communication system

ABSTRACT

In a mobile communication system, an RRM measurement set is set as a collection of cells to become targets on which a UE performs a process of detecting whether or not radio communication is allowed. Among the cells in the RRM measurement set, a CoMP measurement set is set as a collection of cells to become candidates on which the UE performs a process of detecting whether or not coordinated communication (CoMP communication) is allowed. Among the cells of the CoMP measurement set, a CoMP active set is set as a collection of cells to become targets on which the UE performs the process of detecting whether or not CoMP communication is allowed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of 15/624,126, filed Jun.15, 2017, which is a divisional of U.S. Application No. 14/374,744 filedJul. 25, 2014 (now U.S. Pat. No. 9,712,213), which is a National Phaseof PCT/JP2013/051454 filed Jan. 24, 2013, and claims priority toJapanese Patent Application No. 2012-015282 filed Jan. 27, 2012. Theentire contents of each of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a mobile communication system in whicha base station device performs radio communication with a plurality ofmobile terminal devices.

BACKGROUND ART

Commercial service of a wideband code division multiple access (W-CDMA)system among so-called third-generation communication systems has beenoffered in Japan since 2001. In addition, high speed downlink packetaccess (HSDPA) service for achieving higher-speed data transmissionusing a downlink has been offered by adding a channel for packettransmission (high speed-downlink shared channel (HS-DSCH)) to thedownlink (dedicated data channel, dedicated control channel). Further,in order to increase the speed of data transmission in an uplinkdirection, service of a high speed uplink packet access (HSUPA) systemhas been offered. W-CDMA is a communication system defined by the 3rdgeneration partnership project (3GPP) that is the standard organizationregarding the mobile communication system, where the specifications ofRelease 10 version are produced.

Further, 3GPP is studying new communication systems referred to as longterm evolution (LTE) regarding radio areas and system architectureevolution (SAE) regarding the overall system configuration including acore network and a radio access network (hereinafter, also referred toas a network) as communication systems independent of W-CDMA. Thiscommunication system is also referred to as 3.9 generation (3.9 G)system.

In the LTE, an access scheme, a radio channel configuration, and aprotocol are totally different from those of the W-CDMA (HSDPA/HSUPA).For example, as to the access scheme, code division multiple access isused in the W-CDMA, whereas in the LTE, orthogonal frequency divisionmultiplexing (OFDM) is used in a downlink direction and single carrierfrequency division multiple access (SC-FDMA) is used in an uplinkdirection. In addition, the bandwidth is 5 MHz in the W-CDMA, while inthe LTE, the bandwidth can be selected from 1.4 MHz, 3 MHz, 5 MHz, 10MHz, 15 MHz, and 20 MHz per base station. Further, differently from theW-CDMA, circuit switching is not provided but a packet communicationsystem is only provided in the LTE.

In the LTE, a communication system is configured with a new core networkdifferent from the general packet radio service (GPRS) being the corenetwork of the W-CDMA, and thus, the radio access network of the LTE isdefined as a radio access network independent of the W-CDMA network.

Therefore, for differentiation from the W-CDMA communication system, acore network and a radio access network are referred to as an evolvedpacket core (EPC) and an evolved universal terrestrial radio accessnetwork (E-UTRAN), respectively, in the LTE communication system. Alsoin the radio access network, the base station that communicates with amobile terminal (user equipment (UE)) is referred to as an E-UTRAN NodeB(eNB). The EPC functions as a radio network controller that exchangescontrol data and user data with a plurality of base stations. The EPC isalso referred to as an access gateway (aGW). The system formed of theEPC and E-UTRAN is referred to as an evolved packet system (EPS).

Unicast service and evolved multimedia broadcast multicast service(E-MBMS service) are provided in this LTE communication system. TheE-MBMS service is broadcast multimedia service. The E-MBMS service ismerely referred to as MBMS in some cases. Bulk broadcast contents suchas news, weather forecast, and mobile broadcast are transmitted to aplurality of user equipments in the E-MBMS service. This is alsoreferred to as point to multipoint service.

Non-Patent Document 1 (Chapter 4) describes the current decisions by3GPP regarding an overall architecture in the LTE system. The overallarchitecture will be described with reference to FIG. 1 . FIG. 1 is adiagram illustrating the configuration of the LTE communication system.With reference to FIG. 1 , the E-UTRAN is composed of one or a pluralityof base stations 102, provided that a control protocol for a userequipment 101 such as a radio resource control (RRC), and user planessuch as a packet data convergence protocol (PDCP), radio link control(RLC), medium access control (MAC) and physical layer (PHY) areterminated in the base station 102.

The base stations 102 perform scheduling and transmission of a pagingsignal (also referred to as paging messages) notified from a mobilitymanagement entity (MME) 103. The base stations 102 are connected to eachother by means of an X2 interface. In addition, the base stations 102are connected to an evolved packet core (EPC) by means of an S1interface. More specifically, the base station 102 is connected to themobility management entity (MME) 103 by means of an S1_MME interface andconnected to a serving gateway (S-GW) 104 by means of an S1_U interface.

The MME 103 distributes the paging signal to a plurality of or a singlebase station 102. In addition, the MME 103 performs mobility control ofan idle state. When the user equipment is in the idle state and anactive state, the MME 103 manages a list of tracking areas.

The S-GW 104 transmits/receives user data to/from one or a plurality ofbase stations 102. The S-GW 104 serves as a local mobility anchor pointin handover between base stations. Moreover, a PDN gateway (P-GW) isprovided in the EPC. The P-GW performs per-user packet filtering andUE-ID address allocation.

The control protocol RRC between the user equipment 101 and the basestation 102 performs broadcast, paging, RRC connection management, andthe like. The states of the base station and the user equipment in RRCare classified into RRC_IDLE and RRC _CONNECTED. In RRC_1DLE, publicland mobile network (PLMN) selection, system information (SI) broadcast,paging, cell re-selection, mobility, and the like are performed. InRRC_CONNECTED, the user equipment has RRC connection and is capable oftransmitting/receiving data to/from a network. In RRC_CONNECTED, forexample, handover (HO) and measurement of a neighbour cell areperformed.

The current decisions by 3GPP regarding the frame configuration in theLTE system described in Non-Patent Document 1 (Chapter 5) will bedescribed with reference to FIG. 2 . FIG. 2 is a diagram illustratingthe configuration of a radio frame used in the LTE communication system.With reference to FIG. 2 , one radio frame is 10 ms. The radio frame isdivided into ten equally sized sub-frames. The subframe is divided intotwo equally sized slots. The first and sixth subframes contain adownlink synchronization signal (SS) per each radio frame. Thesynchronization signals are classified into a primary synchronizationsignal (P-SS) and a secondary synchronization signal (S-SS).

Multiplexing of channels for multimedia broadcast multicast servicesingle frequency network (MBSFN) and for non-MBSFN is performed on aper-subframe basis. MBSFN transmission is the simulcast transmissiontechnique realized by simultaneous transmission of the same waveformsfrom a plurality of cells. The MBSFN transmission from a plurality ofcells in the MBSFN area is seen as a single transmission by a userequipment. The MBSFN is a network that supports such MBSFN transmission.Hereinafter, a subframe for MBSFN transmission is referred to as MBSFNsubframe.

Non-Patent Document 2 describes a signaling example when MBSFN subframesare allocated. FIG. 3 is a diagram illustrating the configuration of theMBSFN frame. As shown in FIG. 3 , the radio frames including the MBSFNsubframes are allocated per radio frame allocation period. The MBSFNsubframe is a subframe allocated for the MBSFN in a radio frame definedby the allocation period and the allocation offset (radio frameallocation offset), and serves to transmit multimedia data. The radioframe satisfying Equation (1) below is a radio frame including the MBSFNsubframes.

$\begin{matrix}\begin{array}{l}\text{SFN mod radioFrameAllocationPeriod =} \\\text{radioFrameAllocationOffset}\end{array} & \text{­­­(1)}\end{matrix}$

The MBSFN subframe is allocated with six bits. The leftmost bit in FIG.3 defines the MBSFN allocation for the second subframe (#1). The secondbit, third bit, fourth bit, fifth bit, and sixth-bit from the leftdefine the MBSFN allocation for the third subframe (#2), fourth subframe(#3), seventh subframe (#6), eighth subframe (#7), and ninth subframe(#8), respectively. The case where the bit indicates “one” representsthat the corresponding subframe is allocated for the MBSFN.

Non-Patent Document 1 (Chapter 5) describes the current decisions by3GPP regarding the channel configuration in the LTE system. It isassumed that the same channel configuration is used in a closedsubscriber group (CSG) cell as that of a non-CSG cell. Physical channelsare described with reference to FIG. 4 . FIG. 4 is a diagramillustrating physical channels used in the LTE communication system.

With reference to FIG. 4 , a physical broadcast channel (PBCH) 401 is achannel for downlink transmission from the base station 102 to the userequipment 101. A BCH transport block is mapped to four subframes withina 40 ms interval. There is no explicit signaling indicating 40 mstiming.

A physical control format indicator channel (PCFICH) 402 is a channelfor downlink transmission from the base station 102 to the userequipment 101. The PCFICH notifies the number of OFDM symbols used forPDCCHs from the base station 102 to the user equipment 101. The PCFICHis transmitted in each subframe.

A physical downlink control channel (PDCCH) 403 is a channel fordownlink transmission from the base station 102 to the user equipment101. The PDCCH notifies the resource allocation information for downlinkshared channel (DL-SCH) being one of the transport channels shown inFIGS. 5(A) and 5(B) described below, resource allocation information fora paging channel (PCH) being one of the transport channels shown inFIGS. 5(A) and 5(B), and hybrid automatic repeat request (HARQ)information related to DL-SCH. The PDCCH carries an uplink schedulinggrant. The PDCCH carries acknowledgement (Ack) / negativeacknowledgement (Nack) that is a response signal to uplink transmission.The PDCCH is referred to as an L1/L2 control signal as well.

A physical downlink shared channel (PDSCH) 404 is a channel for downlinktransmission from the base station 102 to the user equipment 101. Adownlink shared channel (DL-SCH) that is a transport channel and a PCHthat is a transport channel are mapped to the PDSCH.

A physical multicast channel (PMCH) 405 is a channel for downlinktransmission from the base station 102 to the user equipment 101. Amulticast channel (MCH) that is a transport channel is mapped to thePMCH.

A physical uplink control channel (PUCCH) 406 is a channel for uplinktransmission from the user equipment 101 to the base station 102. ThePUCCH carries Ack/Nack that is a response signal to downlinktransmission. The PUCCH carries a channel quality indicator (CQI)report. The CQI is quality information indicating the quality ofreceived data or channel quality. In addition, the PUCCH carries ascheduling request (SR).

A physical uplink shared channel (PUSCH) 407 is a channel for uplinktransmission from the user equipment 101 to the base station 102. Anuplink shared channel (UL-SCH) that is one of the transport channelsshown in FIGS. 5(A) and 5(B) is mapped to the PUSCH.

A physical hybrid ARQ indicator channel (PHICH) 408 is a channel fordownlink transmission from the base station 102 to the user equipment101. The PHICH carries Ack/Nack that is a response signal to uplinktransmission. A physical random access channel (PRACH) 409 is a channelfor uplink transmission from the user equipment 101 to the base station102. The PRACH carries a random access preamble.

A downlink reference signal (RS) is a known symbol in a mobilecommunication system. The following five types of downlink referencesignals are defined: cell-specific reference signals (CRSs), MBSFNreference signals, data demodulation reference signals (DM-RSs) beingUE-specific reference signals, positioning reference signals (PRSs), andchannel-state information reference signals (CSI-Ss). The physical layermeasurement objects of a user equipment include reference symbolreceived power (RSRP).

The transport channels described in Non-Patent Document 1 (Chapter 5)will be described with reference to FIGS. 5(A) and 5(B). FIGS. 5(A) and5(B) are diagrams illustrating transport channels used in the LTEcommunication system. FIG. 5(A) shows mapping between downlink transportchannels and downlink physical channels. FIG. 5(B) shows mapping betweenuplink transport channels and uplink physical channels.

A broadcast channel (BCH) among the downlink transport channels shown inFIG. 5(A) is broadcast to the entire coverage of a base station (cell).The BCH is mapped to the physical broadcast channel (PBCH).

Retransmission control according to a hybrid ARQ (HARQ) is applied to adownlink shared channel (DL-SCH). The DL-SCH enables broadcast to theentire coverage of the base station (cell). The DL-SCH supports dynamicor semi-static resource allocation. The semi-static resource allocationis also referred to as persistent scheduling. The DL-SCH supportsdiscontinuous reception (DRX) of a user equipment for enabling the userequipment to save power. The DL-SCH is mapped to the physical downlinkshared channel (PDSCH).

The paging channel (PCH) supports DRX of the user equipment for enablingthe user equipment to save power. The PCH is required to broadcast tothe entire coverage of the base station (cell). The PCH is mapped tophysical resources such as the physical downlink shared channel (PDSCH)that can be used dynamically for traffic.

The multicast channel (MCH) is used for broadcast to the entire coverageof the base station (cell). The MCH supports SFN combining of MBMSservices (MTCH and MCCH) in multi-cell transmission. The MCH supportssemi-static resource allocation. The MCH is mapped to the PMCH.

Retransmission control according to a hybrid ARQ (HARQ) is applied to anuplink shared channel (UL-SCH) among the uplink transport channels shownin FIG. 5(B). The UL-SCH supports dynamic or semi-static resourceallocation. The UL-SCH is mapped to the physical uplink shared channel(PUSCH).

A random access channel (RACH) shown in FIG. 5(B) is limited to controlinformation. The RACH involves a collision risk. The RACH is mapped tothe physical random access channel (PRACH).

The HARQ will be described. The HARQ is the technique for improving thecommunication quality of a channel by combination of automatic repeatrequest (ARQ) and error correction (forward error correction). The HARQis advantageous in that error correction functions effectively byretransmission even for a channel whose communication quality changes.In particular, it is also possible to achieve further qualityimprovement in retransmission through combination of the receptionresults of the first transmission and the reception results of theretransmission.

An example of the retransmission method will be described. In a casewhere the receiver fails to successfully decode the received data, inother words, in a case where a cyclic redundancy check (CRC) erroroccurs (CRC=NG), the receiver transmits “Nack” to the transmitter. Thetransmitter that has received “Nack” retransmits the data. In a casewhere the receiver successfully decodes the received data, in otherwords, in a case where a CRC error does not occur (CRC=OK), the receivertransmits “AcK” to the transmitter. The transmitter that has received“Ack” transmits the next data.

Examples of the HARQ system include chase combining. In chase combining,the same data is transmitted in the first transmission andretransmission, which is the system for improving gains by combining thedata of the first transmission and the data of the retransmission inretransmission. Chase combining is based on the idea that correct datais partially included even if the data of the first transmissioncontains an error, and highly accurate data transmission is enabled bycombining the correct portions of the first transmission data and theretransmission data. Another example of the HARQ system is incrementalredundancy (IR). The IR is aimed to increase redundancy, where a paritybit is transmitted in retransmission to increase the redundancy bycombining the first transmission and retransmission, to thereby improvethe quality by an error correction function.

The logical channels described in Non-Patent Document 1 (Chapter 6) willbe described with reference to FIGS. 6(A) and 6(B). FIGS. 6(A) and 6(B)are diagrams illustrating logical channels used in an LTE communicationsystem. FIG. 6(A) shows mapping between downlink logical channels anddownlink transport channels. FIG. 6(B) shows mapping between uplinklogical channels and uplink transport channels.

A broadcast control channel (BCCH) is a downlink channel for broadcastsystem control information. The BCCH that is a logical channel is mappedto the broadcast channel (BCH) or downlink shared channel (DL-SCH) thatis a transport channel.

A paging control channel (PCCH) is a downlink channel for transmittingpaging signals and system information change notifications. The PCCH isused when the network does not know the cell location of a userequipment. The PCCH that is a logical channel is mapped to the pagingchannel (PCH) that is a transport channel.

A common control channel (CCCH) is a channel for transmission controlinformation between user equipments and a base station. The CCCH is usedin a case where the user equipments have no RRC connection with thenetwork. In a downlink direction, the CCCH is mapped to the downlinkshared channel (DL-SCH) that is a transport channel. In an uplinkdirection, the CCCH is mapped to the uplink shared channel (UL-SCH) thatis a transport channel.

A multicast control channel (MCCH) is a downlink channel forpoint-to-multipoint transmission. The MCCH is used for transmission ofMBMS control information for one or several MTCHs from a network to auser equipment. The MCCH is used only by a user equipment duringreception of the MBMS. The MCCH is mapped to the multicast channel (MCH)that is a transport channel.

A dedicated control channel (DCCH) is a point-to-point channel thattransmits dedicated control information between a user equipment and anetwork. The DCCH is used if the user equipment has an RRC connection.The DCCH is mapped to the uplink shared channel (UL-SCH) in uplink andmapped to the downlink shared channel (DL-SCH) in downlink.

A dedicated traffic channel (DTCH) is a point-to-point communicationchannel for transmission of user information to a dedicated userequipment. The DTCH exists in uplink as well as downlink. The DTCH ismapped to the uplink shared channel (UL-SCH) in uplink and mapped to thedownlink shared channel (DL-SCH) in downlink.

A multicast traffic channel (MTCH) is a downlink channel for trafficdata transmission from a network to a user equipment. The MTCH is achannel used only by a user equipment during reception of the MBMS. TheMTCH is mapped to the multicast channel (MCH).

CGI represents a cell global identifier. ECGI represents an E-UTRAN cellglobal identifier. A closed subscriber group (CSG) cell is introduced inthe LTE, and the long term evolution advanced (LTE-A) and universalmobile telecommunication system (UMTS) described below. The CSG cellwill be described below (see Chapter 3.1 of Non-Patent Document 3).

The closed subscriber group (CSG) cell is a cell in which subscriberswho are allowed to use are specified by an operator (also referred to asa “cell for specific subscribers”).

The specified subscribers are allowed to access one or more cells of apublic land mobile network (PLMN). One or more cells in which thespecified subscribers are allowed access are referred to as “CSGcell(s)”. Note that access is limited in the PLMN.

The CSG cell is part of the PLMN that broadcasts a specific CSG identity(CSG ID; CSG-ID) and broadcasts “TRUE” in a CSG indication. Theauthorized members of the subscriber group who have registered inadvance access the CSG cells using the CSG-ID that is the accesspermission information.

The CSG-ID is broadcast by the CSG cell or cells. A plurality of CSG-IDsexist in a mobile communication system. The CSG-IDs are used by userequipments (UEs) for making access from CSG-related members easier.

The locations of user equipments are tracked based on an area composedof one or more cells. The locations are tracked for enabling tracking ofthe locations of user equipments and calling user equipments, in otherwords, incoming calling to user equipments even in an idle state. Anarea for tracking locations of user equipments is referred to as atracking area.

The CSG whitelist is a list that may be stored in a universal subscriberidentity module (USIM) in which all CSG IDs of the CSG cells to whichthe subscribers belong are recorded. The CSG whitelist may be merelyreferred to as a whiltelist or an allowed CSG list as well. As to theaccess of user equipments through a CSG cell, the MME performs accesscontrol (see Chapter 4.3.1.2 of Non-Patent Document 4). Specificexamples of the access of user equipments include attach, combinedattach, detach, service request, and a tracking area update procedure(see Chapter 4.3.1.2 of Non-Patent Document 4).

The service types of a user equipment in an idle state will be describedbelow (see Chapter 4.3 of Non-Patent Document 3). The service types ofuser equipments in an idle state include a limited service, normalservice, and operator service. The limited service includes emergencycalls, earthquake and tsunami warning system (ETWS), and commercialmobile alert system (CMAS) on an acceptable cell described below. Thestandard service (also referred to as normal service) is a publicservice on a suitable cell described below. The operator serviceincludes a service for operators only on a reserved cell describedbelow.

A “suitable cell” will be described below. The “suitable cell” is a cellon which a UE may camp to obtain normal service. Such a cell shallfulfill the following conditions (1) and (2).

(1) The cell is part of the selected PLMN or the registered PLMN, orpart of the PLMN of an “equivalent PLMN list”.

(2) According to the latest information provided by a non-access stratum(NAS), the cell shall further fulfill the following conditions (a) to(d):

-   (a) the cell is not a barred cell;-   (b) the cell is part of a tracking area (TA), not part of the list    of “forbidden LAs for roaming”, where the cell needs to fulfill (1)    above;-   (c) the cell shall fulfill the cell selection criteria; and-   (d) for a cell specified as CSG cell by system information (SI), the    CSG-ID is part of a “CSG whitelist” of the UE, that is, is contained    in the CSG whitelist of the UE.

An “acceptable cell” will be described below. The “acceptable cell” isthe cell on which a UE may camp to obtain limited service. Such a cellshall fulfill the all following requirements (1) and (2).

(1) The cell is not a prohibited cell (also referred to as a “barredcell”).

The cell fulfills the cell selection criteria.

“Barred cell” is indicated in the system information. “Reserved cell” isindicated in the system information.

“Camping on a cell” represents the state where a UE has completed thecell selection / cell reselection process and the UE has selected a cellfor monitoring the system information and paging information. The cellon which the UE camps may be referred to as a “serving cell”.

3GPP is studying base stations referred to as Home-NodeB (Home-NB; HNB)and Home-eNodeB (Home-eNB; HeNB). HNB/HeNB is a base station for, forexample, household, corporation, or commercial access service inUTRAN/E-UTRAN. Non-Patent Document 5 discloses three different modes ofthe access to the HeNB and HNB. Specifically, those are an open accessmode, a closed access mode, and a hybrid access mode.

The respective modes have the following characteristics. In the openaccess mode, the HeNB and HNB are operated as a normal cell of a normaloperator. In the closed access mode, the HeNB and HNB are operated as aCSG cell. The CSG cell is a CSG cell where only CSG members are allowedaccess. In the hybrid access mode, the HeNB and HNB are operated as CSGcells where non-CSG members are allowed access at the same time. Inother words, a cell in the hybrid access mode (also referred to as ahybrid cell) is the cell that supports both the open access mode and theclosed access mode.

In 3GPP, among all physical cell identities (PCIs), there is a range ofPCIs reserved by the network for use by CSG cells (see Chapter 10.5.1.1of Non-Patent Document 1). Division of the PCI range is also referred toas PCI split. The information about PCI split (also referred to as PCIsplit information) is broadcast in the system information from a basestation to user equipments being served thereby. To being served by abase station means to take the base station as a serving cell.

Non-Patent Document 6 discloses the basic operation of a user equipmentusing PCI split. The user equipment that does not have the PCI splitinformation needs to perform cell search using all PCIs, for example,using all 504 codes. On the other hand, the user equipment that has thePCI split information is capable of performing cell search using the PCIsplit information.

Further, 3GPP is pursuing specifications standard of long term evolutionadvanced (LTE-A) as Release 10 (see Non-Patent Documents 7 and 8).

As to the LTE-A system, it is studied that a relay and a relay node (RN)are supported for achieving a high data rate, high cell-edge throughput,new coverage area, and the like. The relay node being a relay device iswirelessly connected to the radio-access network via a cell referred toas a donor cell (hereinafter, also referred to as a “Donor eNB; DeNB”).The network (NW)-to-relay node link shares the same frequency band withthe network-to-UE link within the range of the donor cell. In this case,the UE supporting Release 8 of 3GPP is also connectable to the donorcell. The link between a donor cell and a relay node is referred to as abackhaul link, and the link between the relay node and the UE isreferred to as an access link.

As the method of multiplexing a backhaul link in frequency divisionduplex (FDD), the transmission from a DeNB to an RN is performed at adownlink (DL) frequency band, and the transmission from an RN to a DeNBis performed at an uplink (UL) frequency band. As the method of dividingresources in a relay, a link from a DeNB to an RN and a link from an RNto a UE are time-division multiplexed at one frequency band, and a linkfrom an RN to a DeNB and a link from a UE to an RN are alsotime-division multiplexed at one frequency band. In a relay,accordingly, the transmission of the relay is prevented from interferingthe reception of its own relay.

Not only a normal eNB (macro cell) but also so-called local nodes suchas pico eNB (pico cell), HeNB (HNB, CSG cell), node for hotzone cells,relay node, remote radio head (RRH), and repeater are studied in 3GPP.The network composed of various types of cells as described above isalso referred to as a heterogeneous network (HetNet) in some cases.

The frequency bands (hereinafter, also referred to as “operating bands”)usable for communication have been predetermined in the LTE. Non-PatentDocument 9 describes the frequency bands.

Carrier aggregation (CA) is studied in the LTE-A system, in which two ormore component carriers (CCs) are aggregated to support widertransmission bandwidths up to 100 MHz.

A UE supporting Release 8 or 9 of 3GPP, which supports LTE, is capableof transmission/reception only on one CC corresponding to one servingcell. Meanwhile, it is conceivable that a UE supporting Release 10 of3GPP may have the capability of transmission and reception, onlyreception, or only transmission on a plurality of CCs corresponding to aplurality of serving cells at the same time.

Each CC employs the configuration of Release 8 or 9 of 3GPP, and the CAsupports contiguous CCs, non-contiguous CCs, and CCs in differentfrequency bandwidths. The UE cannot configure the number of uplink CCs(UL CCs) equal to or more than the number of downlink CCs (DL CCs). TheCCs configured by the same eNBs do not need to provide the samecoverage. The CC is compatible with Release 8 or 9 of 3GPP.

In CA, an independent HARQ entity is provided per serving cell in uplinkas well as downlink. A transport block is generated per TTI for eachserving cell. Each transport block and HARQ retransmission are mapped toa single serving cell.

In a case where CA is configured, a UE has single RRC connection with aNW. In RRC connection, one serving cell provides NAS mobilityinformation and security input. This cell is referred to as a primarycell (PCell). In downlink, a carrier corresponding to PCell is adownlink primary component carrier (DL PCC). In uplink, a carriercorresponding to PCell is an uplink primary component carrier (UL PCC).

A secondary cell (SCell) is configured to form a pair of a PCell and aserving cell, in accordance with the UE capability. In downlink, acarrier corresponding to SCell is a downlink secondary component carrier(DL SCC). In uplink, a carrier corresponding to SCell is an uplinksecondary component carrier (UL SCC).

A pair of one PCell and a serving cell configured by one or more SCellsis configured for one UE.

The above-mentioned LTE Advanced (LTE-A) is studied as a furtheradvanced communication system regarding radio areas in 3GPP (seeNon-Patent Documents 7 and 8). The LTE-A is based on the LTEcommunication system regarding radio areas and is configured by additionof several new techniques thereto. The new techniques include thetechnique of supporting wider bands (wider bandwidth extension) and thecoordinated multiple point transmission and reception (CoMP) technique.The CoMP studied for LTE-A in 3GPP is described in Non-Patent Document10.

CoMP is the technique of expanding the coverage of high data rates,improving a cell-edge throughput, and increasing a communication systemthroughput by transmission or reception coordinated among multiplegeographically separated points. The CoMPs are grouped into downlinkCoMP (DL CoMP) and uplink CoMP (UL CoMP).

In DL CoMP, the PDSCH to one user equipment (UE) is transmitted incooperation among multiple points. The PDSCH to one UE may betransmitted from one point among multiple points or may be transmittedfrom points among multiple points. In DL CoMP, a serving cell refers toa single cell that transmits resource allocation over the PDCCH.

Joint processing (JP) and coordinated scheduling (CS) / coordinatedbeamforming (CB) (hereinafter, also referred to as “CS/CB”) are studiedas the DL CoMP method.

For JP, data is available at each point in a CoMP cooperating set. JPsare grouped into joint transmission (JT) and dynamic point selection(DPS). DPS includes dynamic cell selection (DCS). In JT, the PDSCH istransmitted from multiple points, specifically, part of or entire CoMPcooperating set, at a time. In DPS, the PDSCH is transmitted from onepoint in the CoMP cooperating set at a time.

In CS/CB, data is only available in transmission from a serving cell. InCS/CB, user scheduling or beamforming decisions are made withcoordination among cells corresponding to the CoMP cooperating set.

Base stations (NB, eNB, HNB, HeNB), remote radio unit (RRU), remoteradio equipment (RRE), remote radio head (RRH), relay node (RN), and thelike are studied as the units and cells that perform transmission atmultiple points. In some cases, the unit and cell that performcoordinated multiple point transmission are also referred to as amulti-point unit and a multi-point cell, respectively.

PRIOR ART DOCUMENTS Non-Patent Documents

-   Non-Patent Document 1: 3GPP TS 36.300 V10.5.0-   Non-Patent Document 2: 3GPP TS 36.331 V10.3.0-   Non-Patent Document 3: 3GPP TS 36.304 V10.3.0 Chapter 3.1, Chapter    4.3, Chapter 5.2.4-   Non-Patent Document 4: 3GPP TR 23.830 V9.0.0-   Non-Patent Document 5: 3GPP S1-083461-   Non-Patent Document 6: 3GPP R2-082899-   Non-Patent Document 7: 3GPP TR 36.814 V9.0.0-   Non-Patent Document 8: 3GPP TR 36.912 V10.0.0-   Non-Patent Document 9: 3GPP TS 36.101 V10.3.0-   Non-Patent Document 10: 3GPP TR 36.819 V11.0.0

SUMMARY OF INVENTION Problems to Be Solved by the Invention

As described above, the coordinated multiple point transmission andreception (CoMP) technique is studied in 3GPP. The execution of CoMP ona UE expands the high-date-rate coverage, improves a cell-edgethroughput, and increases a throughput in a communication system.However, the CoMP technique has yet to be studied thoroughly in 3GPP.

For example, it is studied to provide some collections of CoMP-relatedcells. Considering, for example, the communication quality in CoMP,power consumption of the UE, and a signaling amount between the UE andthe serving cell, however, the collections currently proposed are notalways sufficient. In the case where only the complicated radio waveenvironment that varies over time is used as selection criteria in themethod of selecting a cell in the collection, a good reception qualityis not always obtained even if CoMP is performed.

There is no discussion on the HO process of a UE being subjected toCoMP. The coordinated process is performed between a plurality of cellsin CoMP. Thus, if the UE is subjected to the HO process while beingsubjected to CoMP, the plurality of cells need to be processed, whichdoes not allow for HO by the conventional HO process. Therefore, thecommunication between the UE and the cell cannot be continued.

The present invention has an object to provide a mobile communicationsystem capable of at least continuing communication depending on thestate of a UE to be subjected to CoMP, and further, capable of obtaininga better communication quality through the execution of CoMP.

Means to Solve the Problems

A mobile communication system according to the present invention is amobile communication system in which a plurality of cells configured toperform radio communication with a movable user equipment device areoperated, wherein: the plurality of cells include a cell configured toperform coordinated communication to perform radio communication withthe user equipment device in a coordinated manner with other cell; amongthe plurality of cells, a serving cell that controls the user equipmentdevice configures a detection target cell set and notifies the userequipment device of the detection target cell set that has beenconfigured, the detection target cell set being a collection of cells tobe subjected to a process of detecting, by the user equipment device,whether or not radio communication is allowed; the mobile communicationsystem includes an adjustment unit that adjusts the coordinatedcommunication; the adjustment unit configures a coordination-enabledcell set and a coordination target cell set and notifies the userequipment device of the coordination-enabled cell set and thecoordination target cell set that have been configured, thecoordination-enabled cell set being a collection of cells to becomecandidates on which the user equipment device performs a process ofdetecting whether or not the coordinated communication is allowed amongthe cells in the detection target cell set, the coordination target cellset being a collection of cells to be subjected to a process ofdetecting whether or not the coordinated communication is allowed amongthe cells in the coordination-enabled cell set; and the user equipmentdevice: (a) performs, when being notified of the coordination targetcell set from the adjustment unit, the process of detecting whether ornot the coordinated communication is allowed on each of the cells in thecoordination target cell set; and (b) performs, when being notified ofthe coordination-enabled cell set and not being notified of thecoordination target cell set from the adjustment unit, the process ofdetecting whether or not the coordinated communication is allowed oneach of the cells in the coordination-enabled cell set.

Effects of the Invention

The mobile communication system according to the present invention iscapable of at least continuing communication depending on the state of auser equipment device to execute coordinated communication, and further,is capable of obtaining a better communication quality through theexecution of coordinated communication.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating the configuration of an LTEcommunication system.

FIG. 2 is a diagram illustrating the configuration of a radio frame usedin the LTE communication system.

FIG. 3 is a diagram illustrating the configuration of an MBSFN frame.

FIG. 4 is a diagram illustrating physical channels used in the LTEcommunication system.

FIGS. 5(A) and 5(B) are diagrams illustrating transport channels used inthe LTE communication system.

FIGS. 6(A) and 6(B) are diagrams illustrating logical channels used inthe LTE communication system.

FIG. 7 is a block diagram showing the overall configuration of an LTEmobile communication system currently under discussion of 3GPP.

FIG. 8 is a block diagram showing the configuration of a user equipment71 of FIG. 7 being a user equipment according to the present invention.

FIG. 9 is a block diagram showing the configuration of a base station 72of FIG. 7 being a base station according to the present invention.

FIG. 10 is a block diagram showing the configuration of an MME unit 73of FIG. 7 being an MME according to the present invention.

FIG. 11 is a block diagram showing the configuration of a HeNBGW 74 ofFIG. 7 being a HeNBGW according to the present invention.

FIG. 12 is a flowchart showing an outline from a cell search to an idlestate operation performed by a user equipment (UE) in the LTEcommunication system.

FIG. 13 is a diagram for describing collections of cells used forperforming CoMP.

FIG. 14 is a diagram for describing the inclusion relation of thecollections of cells used for performing CoMP.

FIG. 15 is a diagram showing an exemplary sequence of a mobilecommunication system in a first embodiment.

FIG. 16 is another diagram showing the exemplary sequence of the mobilecommunication system in the first embodiment.

FIG. 17 is a diagram for describing the inclusion relation between aCoMP active set and other sets.

FIG. 18 is a diagram showing an exemplary sequence of a mobilecommunication system in a second embodiment.

FIG. 19 is a diagram showing an exemplary sequence of a mobilecommunication system in a third embodiment.

FIG. 20 is a diagram showing another exemplary sequence of the mobilecommunication system in the third embodiment.

FIG. 21 is a diagram showing still another exemplary sequence of themobile communication system in the third embodiment.

FIG. 22 is a diagram for describing CoMP-related sets and the RSmeasured by a UE.

FIG. 23 is a diagram for describing the communication quality of cellsin the CoMP-related sets.

FIG. 24 is a diagram showing an exemplary sequence of a mobilecommunication system in a fifth embodiment.

FIG. 25 is a diagram showing an exemplary sequence of a mobilecommunication system in a second modification of the fifth embodiment.

FIG. 26 is a diagram for describing ePDCCH.

FIG. 27 is a diagram showing an exemplary sequence of a mobilecommunication system in a sixth embodiment.

FIG. 28 is another diagram showing the exemplary sequence of the mobilecommunication system in the sixth embodiment.

FIG. 29 is a diagram showing an exemplary sequence of a mobilecommunication system in a seventh embodiment.

FIG. 30 is another diagram showing the exemplary sequence of the mobilecommunication system in the seventh embodiment.

FIG. 31 is still another diagram showing the exemplary sequence of themobile communication system in the seventh embodiment.

FIG. 32 is a diagram showing an exemplary sequence of the mobilecommunication system in the seventh embodiment.

FIG. 33 is a diagram showing an exemplary sequence of the mobilecommunication system in the seventh embodiment.

FIG. 34 is a block diagram for describing a specific example of a cellunified entity.

FIG. 35 is a block diagram for describing a specific example of anothercell unified entity.

FIG. 36 is a diagram showing an exemplary sequence of the mobilecommunication system in the seventh embodiment.

FIG. 37 is another diagram showing the exemplary sequence of the mobilecommunication system in the seventh embodiment.

FIG. 38 is still another diagram showing the exemplary sequence of themobile communication system in the seventh embodiment.

FIG. 39 is a diagram showing an exemplary sequence of the mobilecommunication system in the seventh embodiment.

FIG. 40 is a diagram showing an exemplary sequence of the mobilecommunication system in the seventh embodiment.

FIG. 41 is a diagram showing an exemplary sequence of the mobilecommunication system in the seventh embodiment.

FIG. 42 is another diagram showing the exemplary sequence of the mobilecommunication system in the seventh embodiment.

FIG. 43 is still another diagram showing the exemplary sequence of themobile communication system in the seventh embodiment.

FIG. 44 is a diagram showing an exemplary sequence of the mobilecommunication system in the seventh embodiment.

FIG. 45 is a diagram showing an exemplary sequence of the mobilecommunication system in the seventh embodiment.

FIG. 46 is an exemplary sequence of a mobile communication system in aneighth embodiment.

FIG. 47 is another diagram showing the exemplary sequence of the mobilecommunication system in the eighth embodiment.

FIG. 48 is a diagram showing an exemplary sequence of the mobilecommunication system in the eighth embodiment.

FIG. 49 is a diagram showing an exemplary sequence of a mobilecommunication system in a first modification of the eighth embodiment.

FIG. 50 is another diagram showing the exemplary sequence of the mobilecommunication system in the first modification of the eighth embodiment.

FIG. 51 is a diagram showing an exemplary sequence of the mobilecommunication system in the first modification of the eighth embodiment.

FIG. 52 is another diagram showing the exemplary sequence of the mobilecommunication system in the first modification of the eighth embodiment.

FIG. 53 is a diagram showing an exemplary sequence of a mobilecommunication system in a second modification of the eighth embodiment.

FIG. 54 is another diagram showing the exemplary sequence of the mobilecommunication system in the second modification of the eighthembodiment.

FIG. 55 is a diagram showing an exemplary sequence of a mobilecommunication system in the second modification of the eighthembodiment.

FIG. 56 is a diagram showing an exemplary sequence of a mobilecommunication system in a ninth embodiment.

FIG. 57 is another diagram showing the exemplary sequence of the mobilecommunication system in the ninth embodiment.

FIG. 58 is a diagram showing an exemplary sequence of the mobilecommunication system in the ninth embodiment.

FIG. 59 is another diagram showing the exemplary sequence of the mobilecommunication system in the ninth embodiment.

FIG. 60 is a diagram for describing the concept of CoMP communicationamong a plurality of sub eNB devices and a UE.

FIG. 61 is a diagram for describing the concept of CoMP communicationamong a plurality of sub eNB devices and a UE.

FIG. 62 is a diagram for describing a change of a serving cell in atenth embodiment.

FIG. 63 is a diagram showing an exemplary sequence of a mobilecommunication system in the tenth embodiment.

FIG. 64 is another diagram showing the exemplary sequence of the mobilecommunication system in the tenth embodiment.

FIG. 65 is still another diagram showing the exemplary sequence of themobile communication system in the tenth embodiment.

FIG. 66 is yet still another diagram showing the exemplary sequence ofthe mobile communication system in the tenth embodiment.

FIG. 67 is a diagram showing an exemplary sequence of a mobilecommunication system in a first modification of the tenth embodiment.

FIG. 68 is another diagram showing the exemplary sequence of the mobilecommunication system in the first modification of the tenth embodiment.

FIG. 69 is still another diagram showing the exemplary sequence of themobile communication system in the first modification of the tenthembodiment.

FIG. 70 is yet still another diagram showing the exemplary sequence ofthe mobile communication system in the first modification of the tenthembodiment.

FIG. 71 is a diagram showing an exemplary sequence of a mobilecommunication system in a second modification of the tenth embodiment.

FIG. 72 is another diagram showing the exemplary sequence of the mobilecommunication system in the second modification of the tenth embodiment.

FIG. 73 is still another diagram showing the exemplary sequence of themobile communication system in the second modification of the tenthembodiment.

FIG. 74 is a diagram showing an exemplary sequence of a mobilecommunication system in an eleventh embodiment.

FIG. 75 is a diagram showing an exemplary sequence of a mobilecommunication system in a tenth modification of the eleventh embodiment.

DESCRIPTION OF EMBODIMENTS First Embodiment

FIG. 7 is a block diagram showing an overall configuration of an LTEmobile communication system, which is currently under discussion of3GPP. 3GPP is studying an overall configuration of a system includingclosed subscriber group (CSG) cells (Home-eNodeBs (Home-eNB; HeNB) ofE-UTRAN, Home-NB (HNB) of UTRAN) and non-CSG cells (eNodeB (eNB) ofE-UTRAN, NodeB (NB) of UTRAN, and BSS of GERAN) and, as to E-UTRAN, isproposing the configuration as shown in FIG. 7 (see Chapter 4.6.1 ofNon-Patent Document 1).

FIG. 7 will be described. A user equipment device (hereinafter, referredto as a “user equipment” or “UE”) 71 is capable of performing radiocommunication with a base station device (hereinafter, referred to as a“base station”) 72 and transmits/receives signals through radiocommunication. The base stations 72 are classified into an eNB 72-1 thatis a macro cell and a Home-eNB 72-2 that is a local node. The eNB 72-1has a relatively large-scale coverage as the coverage in a range inwhich communication is allowed with the user equipment (UE) 71. TheHome-eNB 72-2 has a relatively small-scale coverage as the coverage.

The eNB 72-1 is connected to an MME/S-GW unit (hereinafter, alsoreferred to as an “MME unit”) 73 including an MME, S-GW, or MME and S-GWthrough an S1 interface, and control information is communicated betweenthe eNB 72-1 and the MME unit 73. A plurality of MME units 73 may beconnected to one eNB 72-1. The MME unit 73 is equivalent to managementmeans. The MME unit 73 is included in an EPC being a core network. TheeNBs 72-1 are connected to each other by means of an X2 interface, andcontrol information is communicated between the eNBs 72-1.

The Home-eNB 72-2 is connected to the MME unit 73 by means of an S1interface, and control information is communicated between the Home-eNB72-2 and the MME unit 73. A plurality of Home-eNBs 72-2 are connected toone MME unit 73. Or, the Home-eNBs 72-2 are connected to the MME units73 through a Home-eNB Gateway (HeNBGW) 74. The Home-eNBs 72-2 areconnected to the HeNBGW 74 by means of the S1 interface, and the HeNBGW74 is connected to the MME units 73 through an S1 interface.

One or a plurality of Home-eNBs 72-2 are connected to one HeNBGW 74, andinformation is communicated therebetween through an S1 interface. TheHeNBGW 74 is connected to one or a plurality of MME units 73, andinformation is communicated therebetween through an S1 interface.

The MME units 73 and HeNBGW 74 are devices of higher nodes and controlthe connection between the user equipment (UE) 71 and the eNB 72-1 orHome-eNB 72-2 being a base station. The MME units 73, specifically, theMME and S-GW constituting the MME unit 73 and the HeNBGW 74 areequivalent to management means. The MME units 73 and HeNBGW are includedin an EPC being a core network.

Further, 3GPP is currently studying the configuration below. The X2interface between the Home-eNBs 72-2 is supported. In other words, theHome-eNBs 72-2 are connected to each other by means of an X2 interface,and control information is communicated between the Home-eNBs 72-2. TheHeNBGW 74 appears to the MME unit 73 as the eNB 72-1. The HeNBGW 74appears to the Home-eNB 72-2 as the MME unit 73.

The interfaces between the Home-eNBs 72-2 and the MME units 73 are thesame, which are the S1 interfaces, in both cases where the Home-eNB 72-2is connected to the MME unit 73 through the HeNBGW 74 and it is directlyconnected to the MME unit 73. The HeNBGW 74 does not support themobility to the Home-eNB 72-2 or the mobility from the Home-eNB 72-2that spans a plurality of MME units 73. The Home-eNB 72-2 constitutesand supports a single cell.

The base station device supports a single cell alone, such as theHome-eNB 72-2, which is not limited thereto. One base station device maysupport a plurality of cells. In a case where one base station devicesupports a plurality of cells, every cell functions as a base stationdevice.

FIG. 8 is a block diagram showing the configuration of the userequipment 71 of FIG. 7 being a user equipment according to the presentinvention. The transmission process of the user equipment 71 shown inFIG. 8 will be described. First, a transmission data buffer unit 803stores the control data from a protocol processing unit 801 and the userdata from an application unit 802. The data stored in the transmissiondata buffer unit 803 is transmitted to an encoding unit 804 and issubjected to an encoding process such as error correction. There mayexist the data output from the transmission data buffer unit 803directly to a modulating unit 805 without the encoding process. The dataencoded by the encoding unit 804 is modulated by the modulating unit805. The modulated data is output to a frequency converting unit 806after being converted into a baseband signal, and is then converted intoa radio transmission frequency. After that, a transmission signal istransmitted from an antenna 807 to the base station 72.

The user equipment 71 executes the reception process as follows. Theradio signal is received through the antenna 807 from the base station72. The received signal is converted from a radio reception frequencyinto a baseband signal by the frequency converting unit 806 and is thendemodulated by a demodulating unit 808. The demodulated data istransmitted to a decoding unit 809 and is subjected to a decodingprocess such as error correction. Among the pieces of decoded data, thecontrol data is transmitted to the protocol processing unit 801, whilethe user data is transmitted to the application unit 802. A series ofprocesses of the user equipment 71 is controlled by a control unit 810.This means that, though not shown in FIG. 8 , the control unit 810 isconnected to the respective units 801 to 809.

FIG. 9 is a block diagram showing the configuration of the base station72 of FIG. 7 being a base station according to the present invention.The transmission process of the base station 72 shown in FIG. 9 will bedescribed. An EPC communication unit 901 performs datatransmission/reception between the base station 72 and the EPCs (such asMME unit 73 and HeNBGW 74). A communication with another base stationunit 902 performs data transmission/reception to/from another basestation. The EPC communication unit 901 and the communication withanother base station unit 902 respectively transmit/receive informationto/from a protocol processing unit 903. The control data from theprotocol processing unit 903, and the user data and control data fromthe EPC communication unit 901 and the communication with another basestation unit 902 are stored in a transmission data buffer unit 904.

The data stored in the transmission data buffer unit 904 is transmittedto an encoding unit 905 and is then subjected to an encoding processsuch as error correction. There may exist the data output from thetransmission data buffer unit 904 directly to a modulating unit 906without the encoding process. The encoded data is modulated by themodulating unit 906. The modulated data is output to a frequencyconverting unit 907 after being converted into a baseband signal, and isthen converted into a radio transmission frequency. After that, atransmission signal is transmitted from an antenna 908 to one or aplurality of user equipments 71.

The reception process of the base station 72 is executed as follows. Aradio signal from one or a plurality of user equipments 71 is receivedthrough the antenna 908. The received signal is converted from a radioreception frequency into a baseband signal by the frequency convertingunit 907, and is then demodulated by a demodulating unit 909. Thedemodulated data is transmitted to a decoding unit 910 and is thensubjected to a decoding process such as error correction. Among thepieces of decoded data, the control data is transmitted to the protocolprocessing unit 903, EPC communication unit 901, or communication withanother base station unit 902, while the user data is transmitted to theEPC communication unit 901 and the communication with another basestation unit 902. A series of processes by the base station 72 iscontrolled by a control unit 911. This means that, though not shown inFIG. 9 , the control unit 911 is connected to the respective units 901to 910.

The communication with another base station unit 902 is equivalent to anotification unit and an acquisition unit. The transmission data bufferunit 904, encoding unit 905, modulating unit 906, frequency convertingunit 907, antenna 908, demodulating unit 909, and decoding unit 910 areequivalent to a communication unit.

The functions of the Home-eNB 72-2 currently under discussion of 3GPPwill be described below (see Chapter 4.6.2 of Non-Patent Document 1).The Home-eNB 72-2 has the same function as that of the eNB 72-1. Inaddition, the Home-eNB 72-2 has the function of discovering a suitableserving HeNBGW 74 in a case of connection to the HeNBGW 74. The Home-eNB72-2 is connected only to one HeNBGW 74. That is, in a case of theconnection to the HeNBGW 74, the Home-eNB 72-2 does not use the Flexfunction in the S1 interface. When the Home-eNB 72-2 is connected to oneHeNBGW 74, it is not simultaneously connected to another HeNBGW 74 oranother MME unit 73.

The TAC and PLMN ID of the Home-eNB 72-2 are supported by the HeNBGW 74.When the Home-eNB 72-2 is connected to the HeNBGW 74, selection of theMME unit 73 at “UE attachment” is performed by the HeNBGW 74 instead ofby the Home-eNB 72-2. The Home-eNB 72-2 may be deployed without networkplanning. In this case, the Home-eNB 72-2 is moved from one geographicalarea to another geographical area. The Home-eNB 72-2 in this case isaccordingly required to be connected to a different HeNBGW 74 dependingon its location.

FIG. 10 is a block diagram showing the configuration of the MMEaccording to the present invention. FIG. 10 shows the configuration ofan MME 73 a included in the MME unit 73 shown in FIG. 7 described above.A PDN GW communication unit 1001 performs data transmission/receptionbetween the MME 73 a and a PDN GW. A base station communication unit1002 performs data transmission/reception between the MME 73 a and thebase station 72 by means of the S1 interface. In the case where the datareceived from the PDN GW is user data, the user data is transmitted fromthe PDN GW communication unit 1001 to the base station communicationunit 1002 through a user plane communication unit 1003 and is thentransmitted to one or a plurality of base stations 72. In the case wherethe data received from the base station 72 is user data, the user datais transmitted from the base station communication unit 1002 to the PDNGW communication unit 1001 through the user plane communication unit1003 and is then transmitted to the PDN GW.

In the case where the data received from the PDN GW is control data, thecontrol data is transmitted from the PDN GW communication unit 1001 to acontrol plane control unit 1005. In the case where the data receivedfrom the base station 72 is control data, the control data istransmitted from the base station communication unit 1002 to the controlplane control unit 1005.

A HeNBGW communication unit 1004 is provided in the case where theHeNBGW 74 is provided, which performs data transmission/reception of theinterface (IF) between the MME 73 a and the HeNBGW 74 according to aninformation type. The control data received from the HeNBGWcommunication unit 1004 is transmitted from the HeNBGW communicationunit 1004 to the control plane control unit 1005. The processing resultsof the control plane control unit 1005 are transmitted to the PDN GWthrough the PDN GW communication unit 1001. The processing results ofthe control plane control unit 1005 are transmitted to one or aplurality of base stations 72 by means of the S1 interface through thebase station communication unit 1002, and are transmitted to one or aplurality of HeNBGWs 74 through the HeNBGW communication unit 1004.

The control plane control unit 1005 includes a NAS security unit 1005-1,an SAE bearer control unit 1005-2, an idle state mobility managing unit1005-3, and other unit, and performs an overall process for the controlplane. The NAS security unit 1005-1 provides, for example, security of anon-access stratum (NAS) message. The SAE bearer control unit 1005-2manages, for example, a system architecture evolution (SAE) bearer. Theidle state mobility managing unit 1005-3 performs, for example, mobilitymanagement of an idle state (LTE-IDLE state, which is merely referred toas idle as well), generation and control of a paging signal in an idlestate, addition, deletion, update, and search of a tracking area (TA) ofone or a plurality of user equipments 71 being served thereby, andtracking area list (TA list) management.

The MME 73 a begins a paging protocol by transmitting a paging messageto the cell belonging to a tracking area (TA) in which the UE isregistered. The idle state mobility managing unit 1005-3 may manage theCSG of the Home-eNBs 72-2 to be connected to the MME 73 a, CSG-1Ds, anda whitelist.

In the CSG-ID management, the relationship between a user equipmentcorresponding to the CSG-ID and the CSG cell is managed (for example,added, deleted, updated, or searched). For example, the relationship maybe the relationship between one or a plurality of user equipments whoseuser access registration has been performed with a CSG-ID and the CSGcells belonging to this CSG-ID. In the whitelist management, therelationship between the user equipment and the CSG-ID is managed (forexample, added, deleted, updated, or searched). As an example, one or aplurality of CSG-IDs with which user registration has been performed bya user equipment may be stored in the whitelist. The above-mentionedmanagement related to the CSG may be performed by another part of theMME 73 a. A series of processes by the MME 73 a is controlled by acontrol unit 1006. This means that, though not shown in FIG. 10 , thecontrol unit 1006 is connected to the respective units 1001 to 1005.

The function of the MME 73 a currently under discussion of 3GPP will bedescribed below (see Chapter 4.6.2 of Non-Patent Document 1). The MME 73a performs access control for one or a plurality of user equipmentsbeing members of closed subscriber groups (CSGs). The MME 73 arecognizes the execution of paging optimization as an option.

FIG. 11 is a block diagram showing the configuration of the HeNBGW 74 ofFIG. 7 being a HeNBGW according to the present invention. An EPCcommunication unit 1101 performs data transmission/reception between theHeNBGW 74 and the MME 73 a by means of the S1 interface. A base stationcommunication unit 1102 performs data transmission/reception between theHeNBGW 74 and the Home-eNB 72-2 by means of the S1 interface. A locationprocessing unit 1103 performs the process of transmitting, to aplurality of Home-eNBs 72-2, the registration information or the likeamong the data transmitted from the MME 73 a through the EPCcommunication unit 1101. The data processed by the location processingunit 1103 is transmitted to the base station communication unit 1102 andis transmitted to one or a plurality of Home-eNBs 72-2 through the S1interface.

The data only caused to pass through (to be transparent) withoutrequiring the process by the location processing unit 1103 is passedfrom the EPC communication unit 1101 to the base station communicationunit 1102, and is transmitted to one or a plurality of Home-eNBs 72-2through the S1 interface. A series of processes by the HeNBGW 74 iscontrolled by a control unit 1104. This means that, though not shown inFIG. 11 , the control unit 1104 is connected to the respective units1101 to 1103.

The function of the HeNBGW 74 currently under discussion of 3GPP will bedescribed below (see Chapter 4.6.2 of Non-Patent Document 1). The HeNBGW74 relays an S1 application. The HeNBGW 74 terminates the S1 applicationthat is not associated with the user equipment 71 though it is a part ofthe procedures toward the Home-eNB 72-2 and towards the MME 73 a. Whenthe HeNBGW 74 is deployed, the procedure that is not associated with theuser equipment 71 is communicated between the Home-eNB 72-2 and theHeNBGW 74 and between the HeNBGW 74 and the MME 73 a. The X2 interfaceis not set between the HeNBGW 74 and another node. The HeNBGW 74recognizes the execution of paging optimization as an option.

An example of a cell search method in a mobile communication system willbe described next. FIG. 12 is a flowchart showing an outline from a cellsearch to an idle state operation performed by a user equipment (UE) inthe LTE communication system. When starting a cell search, in StepST1201, the user equipment synchronizes the slot timing and frame timingby a primary synchronization signal (P-SS) and a secondarysynchronization signal (S-SS) transmitted from a neighbor base station.

The P-SS and S-SS are collectively referred to as a synchronizationsignal (SS). Synchronization codes, which individually correspond tophysical cell identities (PCIs) assigned per cell, are assigned to thesynchronization signal (SS). The number of PCIs is currently studied in504 ways. These 504 ways are used for synchronization, and the PCIs ofthe synchronized cells are detected (specified).

In Step ST1202, next, the user equipment detects a cell-specificreference signal (CRS) being a reference signal (RS) transmitted fromthe base station per cell and measures the reference signal receivedpower (RSRP). The codes individually corresponding to the PCIs are usedfor the reference signal RS. Separation from another cell is enabled bycorrelation using the code. The code for RS of the cell is derived fromthe PCI specified in Step ST1201, which makes it possible to detect theRS and measure the RS received power.

In Step ST1203, next, the user equipment selects the cell having thebest RS reception quality, for example, cell having the highest RSreceived power, that is, best cell, from one or more cells that havebeen detected up to Step ST1202.

In Step ST1204, next, the user equipment receives the PBCH of the bestcell and obtains the BCCH that is the broadcast information. A masterinformation block (MIB) containing the cell configuration information ismapped to the BCCH over the PBCH. Accordingly, the MIB is obtained byobtaining the BCCH through reception of the PBCH. Examples of the MIBinformation include the downlink (DL) system bandwidth (also referred toas transmission bandwidth configuration (dl-bandwidth)), the number oftransmission antennas, and system frame number (SFN).

In Step ST1205, next, the user equipment receives the DL-SCH of the cellbased on the cell configuration information of the MIB, to therebyobtain a system information block (SIB) 1 of the broadcast informationBCCH. The SIB1 contains the information about the access to the cell,information on cell selection, and scheduling information about otherSIB (SIBk; k is an integer equal to or larger than two). In addition,the SIB1 contains a tracking area code (TAC).

In Step ST1206, next, the user equipment compares the TAC of the SIB1received in Step ST1205 with the TAC portion of a tracking area identity(TAI) in the tracking area (TA) list that has been already possessed bythe user equipment. The tracking area (TA) list is also referred to as aTAI list. TAI is a TA identity and is formed of a mobile country code(MCC), a mobile network code (MNC), and a tracking area code (TAC). MCCis a country code. MNC is a network code. TAC is a TA code number.

In a case where the TAC received in Step ST1205 is identical to the TACincluded in the tracking area (TA) list as a result of the comparison ofStep ST1206, the user equipment enters an idle state operation in thecell. In a case where the TAC received in Step ST1205 is not included inthe tracking area (TA) list as a result of the comparison, the userequipment requires a core network (EPC) including MME and the like tochange a tracking area (TA) through the cell for performing trackingarea update (TAU). The core network updates the tracking area (TA) listbased on an identification number (such as a UE-ID) of the userequipment transmitted from the user equipment with a TAU request signal.The core network transmits the updated tracking area (TA) list to theuser equipment. The user equipment rewrites (updates) the TAC list ofthe user equipment based on the received tracking area (TA) list. Afterthat, the user equipment enters the idle state operation in the cell.

In the LTE, LTE-A, and universal mobile telecommunication system (UMTS),the introduction of a closed subscriber group (CSG) cell is studied. Asdescribed above, access is allowed for only one or a plurality of userequipments registered with the CSG cell. A CSG cell and one or aplurality of user equipments registered with the CSG cell constitute oneCSG. A specific identification number referred to as CSG-ID is added tothe thus constituted CSG. One CSG may contain a plurality of CSG cells.After being registered with any one of the CSG cells, the user equipmentcan access another CSG cell of the CSG to which the registered CSG cellbelongs.

Alternatively, the Home-eNB in the LTE and LTE-A and the Home-NB in theUMTS are used as the CSG cell in some cases. The user equipmentregistered with the CSG cell has a whitelist. Specifically, thewhitelist is stored in the subscriber identity module (SIM) or USIM. Thewhitelist stores the CSG information of the CSG cell with which the userequipment has been registered. Specific examples of the CSG informationmay include CSG-ID, tracking area identity (TAI), and TAC. Any one ofthe CSG-ID and TAC is adequate as long as they are associated with eachother. Alternatively, ECGI is adequate as long as the CSG-ID and TAC areassociated with ECGI.

As can be seen from the above, the user equipment that has no whitelist(including a case where the whitelist is empty in the present invention)is not allowed to access the CSG cell but is allowed to access thenon-CSG cell only. On the other hand, the user equipment which has awhitelist is allowed to access the CSG cell of the CSG-ID with whichregistration has been performed as well as the non-CSG cell.

The HeNB and HNB are required to support various services. For example,in certain service, an operator causes the predetermined HeNB and HNB toregister user equipments therein and permits only the registered userequipments to access the cells of the HeNB and HNB, which increasesradio resources available for the user equipments and enables high-speedcommunication. The operator correspondingly sets a high charge comparedwith a normal service.

In order to achieve the above-mentioned service, the closed subscribergroup (CSG) cell accessible only to the registered (subscribed ormember) user equipments is introduced. A large number of closedsubscriber group (CSG) cells are required to be installed in shoppingmalls, apartment buildings, schools, companies, and the like. Forexample, the following manner of use is required: the CSG cells areinstalled for each store in shopping malls, for each room in apartmentbuildings, for each classroom in schools, and for each section incompanies such that only the users who have registered with therespective CSG cells are permitted to use those CSG cells. The HeNB/HNBis required not only to complement the communication outside thecoverage of the macro cell (area complementing HeNB/HNB) but also tosupport various services as described above (service providingHeNB/HNB). This also leads to a case where the HeNB/HNB is installedwithin the coverage of the macro cell.

As described above, it is studied to support CoMP as a new LTE-Atechnique. Also, collection (set) of cells or points used for performingCoMP is studied. Examples of the collection of cells used for performingCoMP in the present invention include (1) to (5) below. The collectionof points suffices, not limited to the collection of cells. In thefollowing description, the collection of points or cells used forperforming CoMP is collectively referred to as a “CoMP set”.

(1) RRM measurement set. The radio resource management (RRM) measurementset refers to the collection of cells obtained from the measurementdescribed in the specifications of Releases 8 to 10, specifically,cell-specific reference signal (CRS) measurement.

(2) CoMP cooperating set. The CoMP cooperating set refers to thecollection of cells that enable CoMP.

(3) CoMP coordination area (CoMP coordination cells). The CoMPcoordination area refers to a radio area configured by cells that enableCoMP.

(4) CoMP measurement set. The CoMP measurement set refers to acollection of cells which channel state indication (CSI)-RS of the cellis measured to be reported. The CoMP measurement set is selected fromthe RRM measurement set.

(5) CoMP transmission point. The CoMP transmission point refers to acell that transmits data to a UE being subjected to CoMP. The CoMPtransmission point is selected from the CoMP measurement set. If thereis a CoMP active set described below, the CoMP transmission point may beselected from the CoMP active set. If there is no CoMP active setdescribed below, the CoMP transmission point is selected from the CoMPmeasurement set.

The RRM measurement set is equivalent to a detection target cell set.The measurement described in the specifications of Releases 8 to 10,specifically, the CRS measurement is equivalent to the process ofdetecting whether or not radio communication is allowed, which isperformed by a UE.

The CoMP cooperating set is equivalent to a coordination-enabled cellset, which is the collection of cells to become candidates on which theUE performs the process of detecting whether or not coordinatedcommunication (CoMP communication) is allowed. The CoMP measurement setis equivalent to a coordination target cell set, which is the collectionof cells to become targets on which the UE performs the process ofdetecting whether or not CoMP communication is allowed.

The above-mentioned central entity refers to an entity that intensivelyadjusts (coordinates) CoMP performed by one or a plurality of points(see Non-Patent Document 10). The central entity is equivalent to anadjustment unit. The central entity is a logical entity and may bephysically configured in any device. As an example, the central entitymay be configured in the eNB or RRH, or may be configured separatelyfrom the eNB and RRH. Or, the central entity may be configured in theHeNBGW.

FIG. 13 is a diagram for describing collections of cells used forperforming CoMP. FIG. 13 shows RRM measurement sets 1302 byleft-downward hatching by thin diagonal lines, CoMP cooperating sets1303 by textured hatching, CoMP measurement sets 1304 by right-downwardhatching by thick diagonal lines, and CoMP transmission points 1305 byleft-downward hatching by thick diagonal lines.

The RRM measurement sets 1302, the CoMP cooperating sets 1303, the CoMPmeasurement sets 1304, and the CoMP transmission points 1305 are eachconfigured for a UE 1301. FIG. 13 shows the case where the CoMPcooperating set 1303 is included in the RRM measurement set 1302.

FIG. 14 is a diagram for describing the inclusion relation ofcollections of cells used for performing CoMP. FIG. 14 shows an RRMmeasurement set by a circle indicated by reference numeral “1401”, aCoMP measurement set by a circle indicated by reference numeral “1402”,and a CoMP transmission point by a circle indicated by reference numeral“1403”. As shown in FIG. 14 , a part or the whole of the RRM measurementset 1401 is the CoMP measurement set 1402, and a part or the whole ofthe CoMP measurement set 1402 is the CoMP transmission point 1403.

3GPP has disclosed nothing about the procedure of actually performingCoMP. For example, it is not clear how to use the collections of cellsused for performing CoMP, and thus, CoMP cannot be performed. Thisembodiment discloses, to perform CoMP, the methods of using andconfiguring collections of cells, a notification method between a UE anda serving cell, and a procedure thereof.

FIGS. 15 and 16 are diagrams showing an exemplary sequence of a mobilecommunication system in a first embodiment. FIGS. 15 and 16 arecontinuous with each other at a position of a boundary BL1. FIGS. 15 and16 show the sequence when CoMP is performed on a desired UE in a casewhere a central entity is configured in a serving cell. This sequenceshows the case where a central entity is configured in a serving cell,and thus, the central entity and the serving cell are not particularlydifferentiated from each other and are referred to as a serving cell.

In Step ST1501, the serving cell sets an RRM measurement configurationto set a range in which a desired UE is caused to perform RRMmeasurement. Herein, the desired UE is referred to as “UE1”. Forexample, any one or both of a frequency and a report condition are setas the RRM measurement configuration. As the report condition, forexample, an event that triggers the execution of a report is set. Thecell to be measured may be specified and a cell-identity (ID) such as aPCI of the cell may be set as an RRM measurement configuration. Forexample, if the network has set the RRM measurement set for the UE1,this RRM measurement set may be used. Or, a list of neighbor cells(neighbor cell list) may be used as the RRM measurement set.

The RRM measurement configuration, its notification, and measurementreport may be provided for CoMP. The frequency, report condition, cellidentity, or the like suitable for CoMP is set.

As another method, the RRM measurement configuration, its notification,and measurement report for conventional mobility may be used. If theserving cell can use the frequency, report condition, or cell identityset for mobility in CoMP, the serving cell may use the RRM measurementconfiguration, its notification, and measurement report for conventionalmobility. Or, the serving cell may set the frequency, report condition,or cell identity that can be used for mobility as well as for CoMP. Thisallows the RRM measurement configuration, its notification, andmeasurement report to be shared, reducing a signaling amount and acontrol load.

In Step ST1502, the serving cell notifies the UE1 of the RRM measurementconfiguration set in Step ST1501. Dedicated signaling is used innotification of the RRM measurement configuration. RRC signaling is usedas the dedicated signaling.

In Step ST1503, the UE1 performs measurement of CRS (hereinafter, alsoreferred to as “CRS measurement”) in accordance with the received RRMmeasurement configuration. Specifically, as the CRS measurement, the UE1uses the frequency notified in the RRM measurement configuration todetect a cell whose carrier frequency is the notified frequency.

The CRS measurement may be performed until the UE1 receives a change inor a release of the RRM measurement configuration after receiving theRRM measurement configuration. In this case, the CRS measurement may beperformed regularly or periodically. The broken line connecting StepST1503 and Step ST1522 in FIGS. 15 and 16 indicates that the CRSmeasurement is performed until the UE1 receives a change in or a releaseof the RRM measurement configuration after receiving the RRM measurementconfiguration, as described above.

In Step ST1504, if the CRS measurement results of the detected cellagree with the report condition, the UE1 reports the CRS measurementresults to the serving cell in a measurement report message. Forexample, for the cell in which the received power of the CRS (RSRP)becomes not less than the threshold set in the RRM measurementconfiguration, the UE1 notifies the serving cell of the cell identityand the RSRP of this cell. Alternatively, for example, for the cell inwhich a difference between the CRS received power (RSRP) of the detectedcell and the CRS received power (RSRP) of the serving cell becomes notless than the threshold set in the RRM measurement configuration, theUE1 may notify the serving cell of the cell identity and the RSRP ofthis cell. It is not limited to the CRS received power but may be areception quality (reference signal received quality: RSRQ). The CRSmeasurement results may be reported regularly or periodically. The RRMmeasurement configuration and measurement report may include a servingcell. Or, the CRS measurement results of the serving cell may bereported in the measurement report without fail.

In Step ST1505, the serving cell creates an RRM measurement set composedof one or a plurality of cells reported, based on the measurement reportmessage notified from the UE1.

If the RRM measurement set has been provided for the UE1, the servingcell may add, delete, or change cells in the RRM measurement set basedon the message of the measurement report of Step ST1504. Or, the servingcell may associate whether the threshold is exceeded, the received poweror reception quality of the cell at that time with the cell identity ofthe cell in the RRM measurement set, and then record and manage them.

In Step ST1506, the UE1 and the serving cell perform at least any one ofdownlink (DL) and uplink (UL) data communications.

In Step ST1507, the UE1 derives a channel quality indicator (CQI) fromthe CRS and feeds back the CQI to the serving cell.

In Step ST1508, the serving cell decides whether or not to perform CoMP,that is, to turn on or off CoMP, using the CQI received from the UE1.For example, the serving cell decides to perform CoMP if the CQI fallsbelow a predetermined threshold (hereinafter, referred to as a“threshold A”) or decides to stop performing CoMP if the CQI exceeds apredetermined threshold (hereinafter, referred to as a “threshold B”).The threshold A and the threshold B may be provided with a predeterminedoffset to exhibit hysteresis. This allows the serving cell to judgewhether or not to perform CoMP on the UE1. After the process of StepST1508 is complete, the serving cell moves to Step ST1530.

In Step ST1530, the serving cell decides the CoMP measurement set forthe UE 1. In other words, the serving cell selects a CoMP measurementset. Specifically, the serving cell selects cells in the CoMPmeasurement set (hereinafter, also referred to as“in-CoMP-measurement-set cells”). The in-CoMP-measurement-set cells areselected from the cells in the RRM measurement set (hereinafter, alsoreferred to as “in-RRM-measurement-set cells”). The cell identities ofthe cells in the RRM measurement set, the number of cells that can beincluded in the CoMP measurement set, the received power (RSRP) orreception quality (RSRQ) of the reference symbol of the cell(hereinafter, also referred to as “RSRP/RSRQ”), or the like may be usedas an indicator for selection. They may be used with the CQI.

As another indicator for selection, for example, the load of each cellmay be used. The serving cell does not select a cell for the CoMPmeasurement set if the load of that cell is high or selects a cell forthe CoMP measurement set if the load of that cell is low. With the useof the load of each cell with the indicator, whether or not to allowCoMP can be decided depending on the load condition of each cell,improving a throughput as the mobile communication system.

The RRM measurement set, however, may include a cell that does notbelong to a CoMP cooperating set. In this case, CoMP cannot be performedif the cell that does not belong to the CoMP cooperating set is selectedfor a CoMP measurement set. It is therefore useless to select the cellthat does not belong to the CoMP cooperating set for a CoMP measurementset, which may cause a malfunction.

This embodiment limits the cells, which are to be selected for a CoMPmeasurement set, to the cells belonging to the CoMP cooperating set inthe RRM measurement set. This allows only the cells capable of CoMP tobe included in the CoMP measurement set.

If only the serving cell is included as the in-CoMP-measurement-set cellin Step ST1530, the serving cell may judge to stop performing CoMP. Inthat case, the serving cell may decide to release the CoMP measurementconfiguration and notify the UE 1 of the release or may move to theprocess of Step ST1527. If the serving cell is not included in the CoMPmeasurement set as disclosed below, the serving cell may judge not tostop performing CoMP when there is only one in-CoMP-measurement-setcell. The serving cell and the in-CoMP-measurement-set cell may performCoMP. When the process of Step ST1530 is complete, the serving cellmoves to Step ST1509.

In Step ST1509, the serving cell sets a CoMP measurement configurationfor the UE1. For example, the serving cell sets the cell identity of thein-CoMP-measurement-set cell, the CSI-RS configuration of thein-CoMP-measurement-set cell, the configuration of a demodulationreference signal (DM-RS) for the UE1 of the in-CoMP-measurement-setcell, or the like. The cycle at which the CSI-RS is transmitted per cellis set as the CSI-RS configuration.

In Step ST1510, the serving cell notifies the UE1 of the CoMPmeasurement configuration. Dedicated signaling is used in notificationof the CoMP measurement configuration. RRC signaling is used as thededicated signaling.

In Step ST1511, the UE1 that has received the CoMP measurementconfiguration in Step ST1510 sets at least any one of the CSI-RSconfiguration and DM-RS configuration of the in-CoMP-measurement-setcell set in the CoMP measurement configuration.

In Step ST1513, the serving cell causes the CoMP measurement set totransmit the CSI-RS.

In Step ST1512, the UE1 measures the CSI-RS of thein-CoMP-measurement-set cell. For example, the UE1 measures theRSRP/RSRQ of the CSI-RS. In this embodiment, in Step ST1514, the UE1derives the CSI from the measurement value of the CSI-RS. The process ofderiving the CSI in Step ST1514 needs not to be always performed.

The CSI-RS may be measured per cell or per point. The method ofmeasuring the CSI-RS may be preliminarily decided in specifications ormay be included in the CoMP measurement configuration to be notified theUE1 from the serving cell. The measurement method is included in theCoMP measurement configuration to be notified, allowing the measurementmethod to be changed dynamically or semi-statically. This allows forselection of CoMP transmission points suitable for CoMP.

The CSI-RS of the CoMP measurement set may be measured until the UE1receives the release of the CoMP measurement configuration afterreceiving the CoMP measurement configuration. The CSI-RS may be measuredregularly or periodically.

In Step ST1515, the UE1 reports, to the serving cell, the CSI-RSmeasurement results (CSI-RS measurement report) of thein-CoMP-measurement-set cell, for example, the RSRP/RSRQ measurementresults. If deriving the CSI in Step ST1514 as in this embodiment, inStep ST1515, the UE1 reports the CSI derivation results (CSI feedback)to the serving cell with the CSI-RS measurement results. The CSI-RSmeasurement results may be reported regularly or periodically, or may bereported if a predetermined condition is met. The CoMP measurementconfiguration or CSI-RS measurement report may include the serving cell.Or, the CSI-RS measurement results of the serving cell may be reportedin the CSI-RS measurement report without fail.

In Step ST1516, the serving cell decides CoMP transmission points fromthe CSI-RS measurement results (CSI-RS measurement report) reported fromthe UE1, for example, from the RSRP/RSRQ measurement results and the CSIderivation results (CSI feedback). If the CSI derivation results are notreported in Step ST1515, the serving cell decides CoMP transmissionpoints from the CSI-RS measurement results. In this case, otherindicator, for example, the load of each cell or the like may be used.If the load of each cell is high, the serving cell does not make thecells as CoMP transmission points. If the load of each cell is low, theserving cell makes the cells as CoMP transmission points. With the useof the load of each cell as described above, the serving cell can decidewhether or not to perform CoMP depending on the load condition of eachcell, improving a throughput as the mobile communication system. Whenthe process of Step ST1516 is complete, the serving cell moves to StepST1518.

In Step ST1518, the serving cell includes the information indicative ofthe CoMP transmission points in the physical downlink control channel(PDCCH) for the UE1, and then performs scheduling (CoMP scheduling). Theinformation indicative of the CoMP transmission points may be includedin the downlink control information (DCI) of the PDCCH.

The information indicative of the CoMP transmission points may be thecell identities such as PCIs. However, the number of bits requiredincreases for the cell identities such as PCIs, causing a problem thatthe capacity of the PDCCH becomes scarce if the information is includedin the PDCCH.

In order to solve the problem that the capacity of the PDCCH becomesscarce, cells in the CoMP measurement set may be numbered and theresulting numbers may indicate the CoMP transmission points. The numbersare limited to the number of cells in the CoMP measurement set, andthus, the use of the numbers reduces an amount of information. If thenumbers are used, the relationship between the cell identities of thein-CoMP-measurement-set cells and the resulting numbers may be includedin the CoMP measurement configuration set in Step ST1509 to be notifiedthe UE1 from the serving cell in Step ST1510.

In Step ST1517, the UE1 receives the PDCCH from the serving cell andobtains the CoMP transmission point information included in the DCI ofthe PDCCH, to thereby receive the CoMP transmission points. The CoMPmeasurement configuration received in Step ST1510 may be used inreceiving the CoMP transmission points.

In Step ST1519, the UE1 and the serving cell perform CoMPtransmission/reception. The UE1 derives the CSI from the CSI-RS and thenfeeds back the CSI to the serving cell.

In Step ST1520, the serving cell judges whether or not to change theCoMP transmission points. Specifically, the serving cell judges whetheror not to change the CoMP transmission points using the CSI feedbackinformation.

If judging to change the CoMP transmission points, the serving cellselects a cell to be added to the CoMP measurement set or a cell to bedeleted from or changed in the CoMP measurement set, using the CSI-RSmeasurement results of the CoMP measurement set and the above-mentionedother indicator. In this case, the serving cell may use the CSI feedbackinformation of the CoMP transmission points and the CSI-RS measurementresults of the CoMP measurement set together.

The serving cell returns to Step ST1516 after performing the cellselection if judging to change the CoMP transmission points in StepST1520 or moves to Step ST1521 if judging not to change the CoMPtransmission points in Step ST1520.

The serving cell that has performed the cell selection adds, deletes, orchanges the CoMP transmission points in Step ST1516 and then moves toStep ST1518. In Step ST1518, the serving cell includes the informationindicative of the CoMP transmission points after the change in the DCIof the PDCCH for the UE1, and then performs CoMP scheduling.

In Step ST1521, the UE1 and the serving cell perform CoMPtransmission/reception. Also, the UE1 derives the CSI from the CSI-RSand feeds back the CSI to the serving cell.

In Step ST1523, the UE1 that has performed CRS measurement in StepST1522 reports the CRS measurement results to the serving cell in ameasurement report message.

In Step ST1524, the serving cell that has received the measurementreport message changes the RRM measurement set, specifically, changesthe in-RRM-measurement-set cell, as required. If deciding to change theRRM measurement set using the cell identity and the CRS measurementresults information received in the measurement report message, theserving cell selects cells to be added, deleted, or changed to add,delete, or change the RRM measurement set.

If the RRM measurement set is changed in Step ST1524, the CoMPmeasurement set selected from the RRM measurement set may need to bechanged, specifically, the in-CoMP-measurement-set cells may need to beadded, deleted, or changed. In Step ST1525, the serving cell accordinglyjudges whether or not to change the CoMP measurement set. Specifically,the serving cell judges whether or not to change thein-CoMP-measurement-set cells.

If judging to change the CoMP measurement set, specifically, change thein-CoMP-measurement-set cells in Step ST1525, the serving cell returnsto Step ST1530 to perform the process of Step ST1530. In Step ST1510,the serving cell notifies the UE1 of the CoMP measurement configurationchanged in Step ST1530.

In this case, the serving cell may notify all of the CoMP measurementconfiguration or notify a difference with the CoMP measurementconfiguration recently notified. The notification of all of the CoMPmeasurement configuration allows the UE and the network to use the sameCoMP measurement configuration without fail, preventing a malfunction.Meanwhile, the notification of a difference with the CoMP measurementconfiguration recently notified reduces a signaling amount to benotified the UE from the serving cell.

If judging not to change the CoMP measurement set, specifically, changethe in-CoMP-measurement-set cells in Step ST1525, the serving cell movesto Step ST1526.

In Step ST1526, the UE1 and the serving cell continuously perform CoMPtransmission/reception. Also, the UE1 derives the CSI from the CSI-RSand feeds back the CSI to the serving cell.

The serving cell that performs CoMP transmission/reception to/from theUE1 in Step ST1526 decides whether or not to perform CoMP. The servingcell may decide whether or not to perform CoMP using the CSI-RSmeasurement results. The serving cell may perform a similar method usingthe CSI-RS in place of the CQI in the process of Step ST1507. Or, theserving cell may decide whether or not to perform CoMP using the CRSmeasurement results. Or, the serving cell may use the CSI-RS measurementresults and the CRS measurement results.

Considered here is the case where the serving cell decides to releaseCoMP, that is, stop performing CoMP in Step ST1527. In this case, inStep ST1528, the serving cell notifies the UE1 of the release of theCoMP measurement configuration. Dedicated signaling is used innotification of the release of the CoMP measurement configuration. RRCsignaling is used as dedicated signaling.

The serving cell that has notified the UE1 of the release of the CoMPmeasurement configuration in Step ST1528 stops performing CoMP on theUE1. This stops the transmission of the CSI-RS from the CoMP measurementset, the transmission of CoMP transmission point scheduling from theserving cell, and the transmission of data from the CoMP transmissionpoints.

In Step ST1529, the UE1 that has received the release of the CoMPmeasurement configuration releases the setting of the CoMP measurementconfiguration such as the CoMP measurement set. This also stops themeasurement of the CoMP measurement set. The UF1 is not notified ofscheduling of the CoMP transmission points from the serving cell, andaccordingly does not perform CoMP transmission/reception.

This embodiment has disclosed the method of using the collections ofcells, the notification method between the UE and the serving cell, andthe procedure thereof in a case where CoMP is performed. The use of themethods disclosed above allows for performing CoMP.

Second Embodiment

As described in the first embodiment, the UE measures the CSI-RS of eachcell in the CoMP measurement set. Thus, the power consumption of the UEincreases as the number of cells in the CoMP measurement set increases.An increase in UE power consumption can be prevented by reducing thenumber of cells in the CoMP measurement set. However, the number ofcells to become candidates for CoMP transmission points reduces as thenumber of cells in the CoMP measurement set is reduced, causing aproblem that optimum CoMP transmission points cannot be selected.

Although the problem that optimum CoMP transmission points cannot beselected is solved by rapidly and frequently changing the CoMPmeasurement set, the in-CoMP-measurement-set cells are changed throughRRC signaling, hindering a rapid change, which causes a delay. Thechanged CoMP measurement set needs to be frequently notified the UE,leading to a problem that an RRC signaling amount increases.

In order to solve the above-mentioned problem, this embodiment willdisclose to provide a subset of in-CoMP-measurement-set cells. Thisembodiment provides a subset composed of a part or the whole of thein-CoMP-measurement-set cells. Such a subset is referred to as a CoMPactive set.

FIG. 17 is a diagram for describing the inclusion relation between theCoMP active set and other sets. As shown in FIG. 17 , the CoMP activeset is configured such that a part or the whole of the RRM measurementset 1401 is the CoMP measurement set 1402, a part or the whole of theCoMP measurement set 1402 is a CoMP active set 1601, and a part or thewhole of the CoMP active set 1601 is the CoMP transmission point 1403.

The method of selecting cells in the CoMP active set (also referred toas “in-CoMP-active-set cells”) will be disclosed. The in-CoMP-active-setcells are selected from the in-CoMP-measurement-set cells. The followingtwo (1) and (2) will be disclosed as indicators for judging which cellis selected.

(1) The CSI-RS measurement results of the UE are used as the judgmentindicator.

The uplink communication quality transmitted from the UE is used as thejudgment indicator.

As the CSI-RS measurement results being the judgment indicator of (1)above, the RSRP or RSRQ of the CSI-RS may be used or the CSI derivedfrom the CSI-RS measurement value may be used. Or, the RSRP or RSRQ ofthe CSI-RS and the CSI derived from the CSI-RS measurement value may beused together. The use of the CSI-RS measurement results as the judgmentindicator for cell selection shows the communication quality of thePDSCH area to which the data for performing CoMP is mapped, allowing forthe selection of cells suitable for performing CoMP.

As the uplink communication quality being the judgment indicator of (2)above, the measurement results of a sounding reference signal (SRS) maybe used or the measurement results of the RS for PUCCH or PUSCHmodulation may be used. The use of the uplink communication quality asthe judgment indicator for cell selection eliminates the need for the UEto measure and report the CSI. This reduces the power consumption of theUE. In time division duplex (TDD), downlink uses the same frequency bandas that of uplink, allowing for the selection of cells suitable forperforming CoMP also in downlink CoMP.

The judgment indicators of (1) and (2) above may be used together ratherthan being used independently. The cells of the CoMP active set may beselected using the both indicators. Or, those judgment indicators andthe CRS measurement results of the UE may be used together.

The method of notifying the UE of the CoMP active set will be disclosed.The serving cell notifies the UE of the cells in the CoMP active set.The serving cell may notify the CoMP active set as required. Forexample, the serving cell may avoid notifying a CoMP active set if theCoMP active set is not configured. In this case, when not being notifiedof the CoMP active set, the UE may judge that the CoMP active set is notconfigured.

The CoMP active set may be notified through MAC signaling. The use ofMAC signaling allows for the notification of a CoMP active set with alower delay than the use of RRC signaling. Besides, RRC signaling is notrequired, and thus, an RRC signaling amount does not increase bynotification of a CoMP active set.

The information indicative of cells in a CoMP active set may be cellidentities such as the PCIs. The cell identities such as PCIs, however,increase the required number of bits, causing a problem that an overheadin MAC increases if the cell identities are included in MAC signaling.

In order to solve this problem, the in-CoMP-measurement-set cells may benumbered such that the resulting numbers indicate the in-CoMP-active-setcells. The numbers are limited to the number of cells in the CoMPmeasurement set, and accordingly, the use of the numbers reduces theamount of information. These numbers may be the same as the numbers ofthe in-CoMP-measurement-set cells provided for CoMP transmission pointsdisclosed in the first embodiment.

If the numbers are used, the relationship between the cell identities ofthe in-CoMP-measurement-set cells and the resulting numbers may beincluded in the CoMP measurement configuration set in Step ST1509 to benotified the UE1 from the serving cell in Step ST1510.

If the CoMP active set is notified through MAC signaling, for example,the CoMP active set information may be included in a MAC control element(MAC CE) to be notified. There may be provided a bit map indicating, byone bit, whether or not each of the cells in the CoMP measurement set isincluded in the CoMP active set. Or, there may be provided a bit map inan ascending order or a descending order of the numbers of the cells inthe CoMP measurement set. Thus, an amount of information for only thenumber of bits for the number of cells in the CoMP measurement set isrequired.

The case where the cells are included in the CoMP measurement set may bereferred to as “activate (act)”, and the case where the cells are notincluded in the CoMP measurement set may be referred to as “deactivate(deact)”. In other words, the collection of cells to be activated in theCoMP measurement set may be a CoMP active set.

The operation of the UE when being notified of a CoMP active set will bedisclosed. The UE measures the CSI-RS of the cell in the CoMP active setnotified through MAC signaling and reports the measurement results tothe serving cell.

In the case where a CoMP active set is set, the UE may avoid measuringand reporting the CSI-RSs of the cells outside the CoMP active set. Thiseliminates the need for the UE to measure the CSI-RSs of all the cellsin the CoMP measurement set, reducing the power consumption. In thiscase, the CRS measurement and report results of the UE or the uplinkcommunication quality from the UE may be used as the judgment indicatorfor cell selection to be included in the CoMP active set.

As another method, in the case where a CoMP active set is set, the UEmay cause at least any one of the CSI-RS measurement cycle and reportcycle to differ between the cells in the CoMP active set and the cellsoutside the CoMP active set. Specifically, it suffices to make theCSI-RS measurement cycle and report cycle of the cells outside the CoMPactive set longer than the CSI-RS measurement cycle and report cycle ofthe cells in the CoMP active set.

This allows for the use of the CSI-RS measurement results with a shortercycle in selecting CoMP transmission points, whereby the CoMPtransmission points suitable for CoMP can be selected. Meanwhile, theuse of the CSI-RS measurement results with a longer cycle in selecting aCoMP active set reduces the UE power consumption. Thus, the UE powerconsumption can be reduced while allowing for the selection of the CoMPtransmission points suitable for CoMP.

In the case where a CoMP active set is set, the serving cell may notifythe UE, through dedicated signaling, of the setting that the UE avoidsmeasuring and reporting the CSI-RSs of the cells outside the CoMP activeset or the setting that the UE causes at least any one of the CSI-RSmeasurement cycle and report cycle to differ between the cells in theCoMP active set and the cells outside the CoMP active set. RRC signalingmay be used as dedicated signaling. For example, the setting may benotified together when the CoMP measurement configuration is notifiedthe UE. Or, the setting may be made dynamically or semi-statically.

Alternatively, the above-mentioned setting may be semi-staticallydecided in specifications in advance. This allows the UE to judge, whenbeing notified of a CoMP active set through MAC signaling, how tomeasure the CSI-RSs of the cells outside the CoMP active set.

When the CoMP active set is set, the cells outside the CoMP active setmay avoid transmitting the CSI-RS. This eliminates the need forunnecessary transmission from the cells.

When the CoMP active set is set, the cells outside the CoMP active setmay avoid performing CoMP on the UE being a CoMP target.

In the CoMP measurement set, CoMP can be performed on the UE being aCoMP target, requiring the data on the UE, the information relatedthereto and scheduling information to be transmitted/received betweenthe cells in the CoMP measurement set. Therefore, a control load and asignaling load increase on the network if the number of cells in theCoMP measurement set is large.

CoMP is not executed from the cells outside the CoMP active set asdescribed above, suppressing the above-mentioned increases in thecontrol load and signaling load on the network.

In this case, the CSI-RS may be transmitted from the cell outside theCoMP active set, or the UE may measure the CSI-RS from the cell outsidethe CoMP active set. Even in such a case, the data for the UE being aCoMP target, the information related thereto, and scheduling informationneed not to be exchanged on the network by avoiding CoMP from the cellsoutside the CoMP active set. This suppresses increases in the controlload and signaling load on the network.

The method of selecting CoMP transmission points from the cells in theCoMP active set will be disclosed. The serving cell selects CoMPtransmission points using the CSI-RS measurement results reported fromthe UE. If the CoMP active set has not been set, the serving cellselects CoMP transmission points from the cells in the CoMP measurementset. If the CoMP active set has not been set, the serving cell mayselect CoMP transmission points using the CSI-RS measurement results ofthe cells in the CoMP measurement set reported from the UE.

An exemplary sequence for performing CoMP in a case where a CoMP activeset is set will be disclosed. The CoMP active set is decided between thedecision of a CoMP measurement set and the decision of CoMP transmissionpoints. FIG. 18 is a diagram showing an exemplary sequence of a mobilecommunication system in the second embodiment. The sequence shown inFIG. 18 is similar to the sequence shown in FIGS. 15 and 16 , and thus,the same steps will be denoted by the same step numbers and commondescription will be omitted. FIG. 18 shows the sequence for performingCoMP in the case where a CoMP active set is set.

The UEl and the serving cell perform, as a first process, the processesof Steps ST1501 to ST1514 and the process of Step ST1530 shown in FIGS.15 and 16 .

In Step ST1515, the UE1 reports the CSI-RS measurement results to theserving cell. In Step ST1701, the serving cell that has received thereport of the CSI-RS measurement results from the UE1 decides to set aCoMP active set. Specifically, the serving cell decides a cell to beactive among the cells in the CoMP measurement set. The CSI-RSmeasurement results reported from the UE are used in judging to decide acell to be active.

In Step ST1702, the serving cell notifies the UE1 of the CoMP activeset. MAC signaling is used in notification of the CoMP active set.

In Step ST1703, the UE1 that has received the CoMP active set measuresthe CSI-RSs of the cells in the CoMP active set. For example, the UElmeasures the RSRP/RSRQ of the CSI-RS.

The CSI-RS may be measured in Step ST1703 per cell or per point. TheCSI-RS measurement method may be preliminarily decided in specificationsor may be included in the CoMP measurement configuration to be notifiedthe UE from the serving cell. The measurement method is included in theCoMP measurement configuration to be notified, allowing for dynamic orsemi-static change of the measurement method. This enables the selectionof CoMP transmission points suitable for CoMP.

The CSI-RS of the CoMP active set may be measured until the UE1 receivesthe release of the configuration of the CoMP active set after receivingthe configuration of the CoMP active set. Or, the CSI-RS of the CoMPactive set may be measured until all the in-CoMP-active-set cells arerendered deactive. The CSI-RS may be measured regularly or periodically.

In Step ST1704, the UE1 derives the CSI from the CSI-RS measurementvalue. The CSI derivation process in Step ST1704 may not to beperformed.

In Step ST1705, the UE1 reports, to the serving cell, the CSI-RSmeasurement results (CSI-RS measurement report) of thein-CoMP-active-set cells, for example, the RSRP/RSRQ measurement resultsand the CSI derivation results (CSI feedback). If the above-mentionedCSI derivation process in Step ST1704 is not performed, the CSIderivation results are not reported. The CSI-RS measurement results maybe reported regularly, may be reported periodically, or may be reportedif a predetermined condition is met. The CoMP active set and the CSI-RSmeasurement report may include the serving cell. Or, the CSI-RSmeasurement results of the serving cell may be reported in the CSI-RSmeasurement report without fail.

In Step ST1516, the serving cell decides CoMP transmission points fromthe reported CSI-RS measurement results, for example, the RSRP/RSRQmeasurement results and the CSI derivation results. Or, the serving cellmay use the indicator such as a cell load together. If the CSIderivation results are not reported in Step ST1705, the serving celldecides CoMP transmission points from the CSI-RS measurement results.

The UE1 that has ended the process of Step ST1705 and the serving cellthat has ended the process of Step ST1516 perform, as a second process,the processes of Steps ST1517 to ST1529 shown in FIGS. 15 and 16 .

The method disclosed in this embodiment only needs the UE to, at least,measure the CSI-RSs of the in-CoMP-active-set cells, reducing the powerconsumption.

The UE is notified through MAC signaling, allowing for setting of a CoMPactive set with a low delay. This suppresses an increase in RRCsignaling amount, allowing for the selection of CoMP transmission pointssuitable for CoMP.

Therefore, CoMP becomes executable, which is suitable for UE movementand rapid fluctuations in radio wave environment. This expands ahigh-data-rate coverage, improves a cell-edge throughput, and increasesa throughput in the communication system.

Third Embodiment

R1-113295 (hereinafter, referred to as “Reference 1”) by 3GPP disclosesthat according to Releases 8, 9, and 10, the RRM measurement set ismanaged based on the CRS measurement results from one UE.

It is also disclosed that an additional RRM measurement mechanism isnecessary for selecting a CoMP measurement set.

It is further disclosed that as an additional RRM measurement mechanism,the use of both of the CRS based RSRP/RSRQ measurement, that is, anormal RRM measurement and the CSI-RS based CQI, the use of the SRS, andthe use of CSI-RS based RSRP/RSRQ measurement.

R1-113064 (hereinafter, referred to as “Reference 2”) by 3GPP disclosesthat as the method of selecting CoMP transmission points, the networkselects CoMP transmission points based on the CSI-RS measurement resultsof the cells in the CoMP measurement set by the UE.

As described above, as to CoMP, the use of the results of CRS or CSI-RSmeasurement by the UE is studied as the method of selecting a CoMPmeasurement set and CoMP transmission points.

In the case where the CRS or CSI-RS measurement results by the UE areused, there arises a problem that depending on a location, a goodreception quality cannot be obtained even if CoMP is performed using themultiple input multiple output (MIMO) technique via a plurality ofantenna ports. This is because effects of, for example, an interferencefrom other many cells, a delay, a phase, and power of each path, therelation among the paths, and a multi-path cannot be evaluatedaccurately, whereby cells suitable for CoMP cannot be selected.

In order to solve the problem that cells suitable for CoMP cannot beselected, this embodiment uses the location information being theinformation related to the UE location to select cells in the set (alsoreferred to as “in-set cells”) in a CoMP set.

Described here is the case where the UE location information is used toselect cells in the set being the CoMP measurement set. The entity ordevice that selects a CoMP measurement set, specifically,in-CoMP-measurement-set cells obtains the location information of the UEto be subjected to CoMP.

The CoMP measurement set is selected using the obtained locationinformation. For example, in the sequence shown in FIGS. 15 and 16 , theserving cell obtains the location information of the UE1 beforeperforming the process of Step ST1530. In Step ST1530, the serving cellselects a CoMP measurement set using the obtained location information.The serving cell can recognize the positional relationship between thecell and the UE by obtaining the UE location information. Therefore, aCoMP measurement set can be selected using the indicator decidedgeographically, namely, the positional relationship, rather than usingthe varying indicator such as the radio wave environment. This allowsfor the selection of a CoMP measurement set more suitable for CoMP.

Not only the UE location information but also the CRS measurementresults reported from the UE may be used to select a CoMP measurementset. Or, the CSI-RS measurement results may be used together. Or, theindicator such as a cell load may be used together. The above-mentionedcombination of the varying indicator and the geographical indicatorallows for the support for a dynamic time variance, and further allowsfor the selection of a CoMP measurement set more suitable for CoMP.

As disclosed in TS23.271 V10.2.0 (hereinafter, referred to as “Reference3”) by 3GPP, the mobile communication system has the function referredto as a location service (LCS). The LCS is the function aimed forestimating the location of a user equipment device for the purpose of,for example, commercial services using location information, managementof a radio communication system, emergency location identification, andlocation identification of a user equipment device for legal reasonssuch as a criminal investigation.

Examples of the method of estimating the location of a user equipmentdevice include the LTE positioning protocol (LPP) disclosed in TS36.305V10.3.0 (hereinafter, referred to as “Reference 4”) by 3GPP.

The methods disclosed in References 3 and 4 may be used as the method ofobtaining the UE location information by the entity that selects a CoMPmeasurement set. In these methods, however, the evolved serving mobilelocation centre (E-SMLC) being the entity that manages the LCS includingthe LPP manages the UE location information. The UE location informationis accordingly notified the E-SMLC, and thus, the entity that selects aCoMP measurement set normally cannot obtain the UE location information.

This embodiment will disclose the method in which the entity thatselects a CoMP measurement set obtains the UE location information.

The entity that selects a CoMP measurement set receives a message bywhich the UE notifies the E-SMLC of the location information of its ownUE to retrieve only the information related to the UE location.

FIG. 19 is a diagram showing an exemplary sequence of a mobilecommunication system in a third embodiment. FIG. 19 shows the sequencein which the entity that selects a CoMP measurement set obtains the UElocation information. In this sequence, the entity that selects a CoMPmeasurement set is a serving cell.

In Step ST1801, the E-SMLC notifies the MME of a request locationinformation message.

In Step ST1802, the MME notifies the serving cell of the receivedrequest location information message as a NAS message.

In Step ST1803, the serving cell forwards the received request locationinformation message to the UE.

In Step ST1804, the UE includes the location information of its own UEin the provide location information message and then notifies theserving cell. The UE location information may be obtained using, forexample, a global positioning system (GPS).

The serving cell that has received the provide location informationmessage retrieves only the information related to the UE location of theprovide location information message. It suffices that the serving cellstores the thus obtained UE location information.

In Step ST1805, the serving cell notifies the MME of the receivedprovide location information message.

In Step ST1806, the MME notifies the E-SMLC of the received providelocation information message.

The request location information message is notified the UE via the MMEand the serving cell. The provide location information message isnotified the E-SMLC via the serving cell and the MME. The NAS message isused between the MME and the serving cell and between the serving celland the UE.

The serving cell receives the message type information of the NASmessage from the NAS message received from the UE in Step ST1804 toretrieve only the information related to the UE location. If the messagetype information of the NAS message indicates the information related tothe LPP or LCS, the serving cell may receive a NAS message and retrievethe information related to the UE location. This eliminates the need forreceiving and retrieving all the NAS messages notified from the UE,reducing the power consumption and lowering a delay at the serving cell.The “generic message container type” information may be used as themessage type information of the NAS message.

The location information may be provided from the UE to the E-SMLC inSteps ST1804 to ST1806 regularly or periodically, as shown in StepsST1807 to ST1809.

In this case, the serving cell successively receives the informationrelated to the UE location from the provide location information messagefrom the UE and updates the UE location information obtained bydecoding. This allows the serving cell to always obtain the latest UElocation information. Thus, the serving cell can always use the latestUE location information when selecting a CoMP measurement set.

Another method in which the entity that selects a CoMP measurement setobtains the UE location information will be disclosed.

The entity that selects a CoMP measurement set is configured to have theLCS client functionality. As an example, the RRC of the serving cell mayhave the LCS client functionality.

This allows the entity that selects a CoMP measurement set to obtain thedesired UE location information from the E-SMLC as required.

FIG. 20 is a diagram showing another exemplary sequence of the mobilecommunication system in the third embodiment. FIG. 20 shows the sequencein which the entity that selects a CoMP measurement set having the LCSclient functionality obtains the UE location information. In thissequence, the serving cell has the entity that selects a CoMPmeasurement set.

In Step ST1901, the serving cell having the LCS client functionalitynotifies the E-SMLC of the request location information message of adesired UE via the MME. The S1 message may be used in the notificationfrom the serving cell to the MME. The serving cell has the LCS clientfunctionality and is thus capable of requesting the desired UE locationinformation from the E-SMLC.

In Step ST1902, the E-SMLC notifies the UE of the received requestlocation information message. The method shown in FIG. 19 may be used asthis notification method.

In Step ST1903, the UE includes the location information of its own UEin the provide location information message and then notifies the E-SMLCvia the serving cell and the MME. The NAS message may be used in thenotification from the UE to the MME.

In Step ST1904, the E-SMLC notifies the serving cell being a requestlocation information source of the provide location information messagereceived from the desired UE. This allows the serving cell to obtain thedesired UE location information.

The location information may be provided from the UE to the E-SMLC inStep ST1903 and the location information may be provided from the E-SMLCto the serving cell in Step ST1904 regularly or periodically as shown inSteps ST1905 and ST1906.

In this case, the serving cell may successively receive the informationrelated to a UE location from the provide location message from the UEto update the obtained UE location information. This allows the servingcell to always obtain the latest UE location information. The servingcell can accordingly use the latest UE location information whenselecting a CoMP measurement set.

Still another method in which the entity that selects a CoMP measurementset obtains the UE location information will be disclosed.

The MME has the LCS client functionality, and the entity that selects aCoMP measurement set requests the information related to the UE locationfrom the MME. This allows the entity that selects a CoMP measurement setto obtain the desired UE location information from the E-SMLC asrequired.

FIG. 21 is a diagram showing still another exemplary sequence of themobile communication system in the third embodiment. FIG. 21 shows thesequence in which the entity that selects a CoMP measurement setrequests the information related to the UE location from the MME toobtain the UE location information, where the MME has the LCS clientfunctionality. In this sequence, the entity that selects a CoMPmeasurement set is the serving cell.

In Step ST2001, the serving cell notifies the MME of a message forrequesting the provision of desired UE location information. In otherwords, the serving cell that needs to be provided with the desired UErequest location information requests the MME to provide the desired UElocation information. The S1 message may be used in the notificationfrom the serving cell to the MME. The message for requesting theprovision of the desired UE location information may be newly providedas the S1 message.

In Step ST2002, the MME notifies the E-SMLC of a request locationinformation message. The MME has the LCS client functionality, and isthus capable of requesting the desired UE location information from theE-SMLC. The MME may receive a message for requesting the provision ofthe desired UE location information from an appropriate cell to activatethe request location information message of the desired UE for theE-SMLC.

In Step ST2003, the E-SMLC notifies the UE of the request locationinformation message. The method shown in FIG. 19 may be used as thisnotification method.

In Step ST2004, the UE includes the location information of its own UEin the provide location information message and then notifies the E-SMLCvia the serving cell and the MME. The NAS message may be used in thenotification from the UE to the MME.

In Step ST2005, the E-SMLC notifies the MME being a request locationinformation source of the provide location information message receivedfrom the desired UE.

In Step ST2006, the MME notifies the cell that has requested theprovision of the location information, here, the serving cell, of theinformation related to the desired UE location included in the receivedprovide location information message as a response to the request toprovide the location information (hereinafter, also referred to as a“location information response”). This allows the serving cell to obtainthe desired UE location information.

As shown in Steps ST2007 and ST2008, the location information may beregularly or periodically provided from the UE to the MME in StepsST2004 and ST2005.

The process of Step ST2005 may urge the location information responsefrom the MME to the serving cell in Step ST2006 to be regularly orperiodically performed as shown in Step ST2009.

In this case, the serving cell may successively receive the informationrelated to the UE location from the provide location message from the UEto update the UE location information obtained by decoding. This allowsthe serving cell to always obtain the latest UE location information.Thus, the serving cell is capable of always using the latest UE locationinformation when selecting a CoMP measurement set.

The following four (1) to (4) will be disclosed as the method ofselecting a CoMP measurement set using the UE location informationobtained by the entity that selects a CoMP measurement set.

(1) At least a cell closest to the latest UE location is selected.

Top k cells are selected starting from the cell positioned closest tothe latest UE location, where k is a natural number and may be decidedin advance.

A cell having a distance from the latest UE location that is smallerthan a predetermined threshold is selected, where the predeterminedthreshold may be decided in advance.

Combination of (1) to (3) above.

Although the latest location is derived based on the latest UE locationinformation in the methods (1) to (4) above, a current location may bederived from the past and latest UE location information. The thusobtained results may be the UE location.

The above-mentioned methods may use the cell location information. Theentity that selects a CoMP measurement set may obtain the locationinformation of a neighbor cell in advance. Examples of the neighbor cellinclude a neighbor cell capable of CoMP and a cell in a CoMP cooperatingset. Or, the neighbor cell may be not limited to a cell capable of CoPM.Each cell notifies the operation administration and maintenance (OAM) ofthe location on its own cell recognized by, for example, GPS. The entitythat selects a CoMP measurement set obtains the location information ofthe neighbor cell from the OAM. Thus, the entity that selects a CoMPmeasurement set may notify the OAM of a message for requesting thelocation information of a neighbor cell. If the E-SMLC manages the celllocation information, the entity that selects a CoMP measurement set mayobtain the location information of a neighbor cell from the E-SMLC. Themethod in which the entity that selects a CoMP measurement set obtainsthe UE location information, disclosed in this embodiment, is applicableas this method. This allows for the selection of a CoMP measurement setusing the UE location information and the cell location information.

Not only the UE location information but also the CRS measurementresults or CSI-RS measurement results reported from the UE may be usedtogether in selecting a CoMP measurement set. Or, indicators such as acell load may be used together. The dynamic time variations can besupported through the combination of a varying indicator and ageographical indicator, allowing for the selection of a CoMP measurementset more suitable for CoMP.

The methods disclosed in this embodiment are applicable to the selectionof an RRM measurement set, specifically, the cells included in the RRMmeasurement set.

The methods disclosed in this embodiment are applicable to the selectionof a CoMP active set, specifically, the cells included in the CoMPactive set.

The methods disclosed in this embodiment are applicable to the selectionof CoMP transmission points.

Fourth Embodiment

Reference 1 discloses the following four methods (a) to (d) based onwhat reference signal (RS) a CoMP measurement set is selected: (a)judgment is made based on an RRM measurement report, namely, RSRP/RSRQof the CRS; (b) judgment is made based on the CSI feedback informationand the RSRP/RSRQ of the CRS; (c) judgment is made based on theSRS/PUCCH/PUSCH; and (d) judgment is made based on the RSRP/RSRQ of theCSI-RS.

Reference 2 discloses that in-CoMP-measurement-set cells are selectedbased on a predetermined threshold (RSRP/RSRQ) or a fixed measurementset size (N).

However, Reference 2 discloses nothing about the method of deciding thevalue of the fixed measurement set size (N). The number of cells thatneed CSI-RS measurement increases as the measurement set size (N)increases. Thus, the UE has problems such as increases in circuit size,power consumption, and cost.

In order to solve the above-mentioned problems, the measurement set size(N) may be an individual value per UE. This allows for setting of anoptimum measurement set size per UE.

In this case, the number of cells (Nu) capable of CoMP is included inthe UE capability, and the UE notifies the network of the number ofcells (Nu) capable of CoMP as capability information. Specifically, thenumber of cells (Nu) capable of CoMP may be included in an attach or aTAU message to be notified. The number of cells capable of CSI-RSmeasurement may be the number of cells (Nu) capable of CoMP. The networkstores the number of cells (Nu) capable of CoMP.

The network notifies the central entity of the number of cells (Nu)capable of CoMP. Or, the central entity may request the network tonotify the number of cells (Nu) capable of CoMP. This allows the centralentity to recognize the number of cells (Nu) capable of CoMP on adesired UE.

The central entity uses the number of cells (Nu) capable of performingCoMP on a UE to select a CoMP measurement set for a desired UE. Forexample, the measurement set size (N) may be the number of cells (Nu)capable of performing CoMP on a UE. Or, the measurement set size (N) maybe made smaller than the number of cells (Nu) capable of performing CoMPon a UE.

As a result, the cells capable of CoMP can be limited for low-cost UEs,preventing increases in circuit size, power consumption, and cost. Themeasurement set size can be optimized depending on the UE capability, sothat CoMP can be performed without increasing the circuit size, powerconsumption, and cost.

In the method disclosed in Reference 2, the measurement set size (N) isfixed. In the case where, for example, cells are installed densely, theUE located at the coverage edge can obtain a desired reception qualityby being subjected to CoMP by a small number of cells.

The situation in which a desired reception quality can be obtained witha small number of cells as described above has such a drawback thatwaste is created in power consumption of the UE, the serving cell, orthe in-CoMP-measurement-set cell if a measurement set size (N) is largerthan the small number of cells with which a desired reception qualitycan be obtained. The UE needs to measure the CSI-RS of an unnecessarycell, whereby waste is created in power consumption. Also, in the cellsin the CoMP measurement set, the unnecessary cell has to transmit theCSI-RS, and thus, waste is created in power consumption.

In order to solve such a problem that waste is created in powerconsumption, this embodiment changes the value of a measurement set size(N) (hereinafter, also referred to as an “N value”) based on thereception quality. It suffices to reduce the N value for a goodreception quality from the UE or increase the N value for a poorreception quality from the UE.

In order to change the N value, the threshold may be set for thereception quality. For example, thresholds A and B are set for thereception quality such that the N value takes a maximum value of themeasurement set size (N) Nmax (N=Nmax) if the reception quality from theUE being subjected to CoMP is not larger than the threshold A. If thereception quality is larger than the threshold A and is not larger thanthe threshold B, the N value is a value obtained by integer-converting avalue obtained by dividing Nmax by 2 (N=int(Nmax/2)). If the receptionquality is larger than the threshold B, the N value is “1” (N=1).

Through the above, the number of cells in the CoMP measurement set canbe changed based on the reception quality from the UE, suppressing anincrease in power consumption.

Although the N value is “1” (N=1) if the reception quality is largerthan the threshold B in this embodiment, CoMP can be stopped as long asthere is one radio link having a good reception quality. For example,the execution of CoMP may be stopped if only the serving cell isincluded as the in-CoMP-measurement-set cell. If thein-CoMP-measurement-set cell is not the serving cell, CoMP may bestopped by the method disclosed in a ninth embodiment described belowsuch that a UE to become a target is subjected to HO, that is, is causedto change a cell to the cell having a good reception quality.

The N value may be changed based on an average value of the receivedqualities from the UE during a predetermined period. This allows the Nvalue to be changed without being affected by temporal variations inreception quality. Thus, the CoMP operation can be performed stably.

The method disclosed in this embodiment is applicable to the selectionof a CoMP active set, specifically, cells included in a CoMP active set.

The method disclosed in this embodiment is applicable to the selectionof CoMP transmission points.

The method disclosed in this embodiment is applicable to the selectionof an RRM measurement set. The UE measures the CRS in the RRMmeasurement set.

There is no discussion in Reference 2 or 3GPP as to whether or not theserving cell is included in the CoMP measurement set. For this reason,it is unclear how to handle the serving cell, whereby CoMP cannot beperformed.

This embodiment will disclose the following three methods (1) to (3)regarding how to handle the serving cell.

(1) The serving cell is also included in handling of the CoMPmeasurement set. In other words, the method of selecting a CoMPmeasurement set is applied. For example, in the case where CoMPmeasurement set includes the serving cell, the serving cell may beinadvertently deleted from the CoMP measurement set if the CSI-RSmeasurement value of the serving cell by the UE deteriorates. Even ifthe serving cell is deleted from the CoMP measurement set, however, theCoMP to be performed on a UE being served thereby can be performed byany other cell in the CoMP measurement set. Therefore, there arises noproblem if the serving cell is also included in handling of the CoMPmeasurement set. The serving cell is included in handling of the CoMPmeasurement set, simplifying the control of the CoMP measurement set.

(2) The CoMP measurement set does not include the serving cell. Thisenables the CoMP measurement set and the serving cell to be handleddifferently, allowing for flexible control. In this case, the UE maymeasure the CSI-RS of the serving cell irrespective of the CoMPmeasurement set. The serving cell may notify the UE of the CoMPmeasurement configuration of its own cell irrespective of the CoMPmeasurement set. Dedicated signaling may be used in this notification.Dedicated signaling may be RRC signaling. The CSI-RS measurement resultsof the serving cell by the UE may be reported to the serving cell. Thesetting of the report method may be notified the UE with the CoMPmeasurement configuration of its own cell. This method can solve theproblem that in the method (1) above, the measurement using the CSI-RSof the serving cell cannot be performed when the serving cell is deletedfrom the CoMP measurement set. In this method, the serving cell is notincluded in the CoMP measurement set but may be the cell capable ofCoMP. The CoMP transmission cell may be selected from thein-CoMP-measurement-set cells and the serving cell. This is allowedbecause the measurement using the CSI-RS of the serving cell isperformed.

(3) The CoMP measurement set includes the serving cell without fail.Differently from the method (1) above, the serving cell is included inthe CoMP measurement set without fail, so that the CSI-RS of the servingcell is measured in accordance with the handling of the CoMP measurementset, leading to easy control. In this case, the serving cell is notcounted in the number N of the CoMP measurement set but may be includedin the CoMP measurement set without fail. Or, the serving cell may beincluded in the CoMP measurement set without fail irrespective of apredetermined threshold for including the serving cell in the CoMPmeasurement set. This allows the UE to perform measurement using theCSI-RS of the serving cell. The method (1) above can solve the problemthat the measurement using the CSI-RS of the serving cell cannot beperformed if the serving cell is deleted from the CoMP measurement set.

The methods disclosed in this embodiment are applicable to the selectionof a CoMP active set, specifically, cells included in the CoMP activeset.

The methods disclosed in this embodiment are applicable to the selectionof an RRM measurement set. The UE measures the CRS in the RRMmeasurement set.

Fifth Embodiment

When the UE being subjected to CoMP moves, the reception quality of theserving cell may degrade, which requires switching of the serving cell.R1-113092 (hereinafter, referred to as “Reference 5”) by 3GPP disclosesto use an RRM measurement report for mobility control. If the RRMmeasurement report is used for mobility control when the UE beingsubjected to CoMP moves, the following problem arises.

FIG. 22 is a diagram for describing sets related to CoMP and an RS to bemeasured by the UE. The cells in the RRM measurement set are normallyconfigured through RRM measurement by the UE, and thus, the RSRP/RSRQ ofthe CRS is measured. As described above, the CoMP measurement set is thecollection of cells whose CSI-RS is measured and reported by the UE.Thus, the RSRP/RSRQ of the CSI-RS is measured by the UE for the cells ina CoMP measurement set. The cells in the CoMP active set are similar tothe cells in the CoMP measurement set, though not shown. The CoMPtransmission point is a cell that actually transmits data to the UE, andthus, the CSI-RS thereof is measured by the UE. The CSI derived from theCSI-RS measurement results by the UE is fed back to the serving cell.

FIG. 23 is a diagram for describing the communication qualities of thein-set cells related to CoMP. FIG. 23 shows the cell numbers in the setrelated to each CoMP and the communication quality. With reference toFIG. 23 , the communication quality increases toward the top of FIG. 23and the communication quality decreases toward the bottom thereof.

In the RRM measurement set, cells are ranked based on the RSRP/RSRQ ofthe CRS by the UE being a communication quality. In the example shown inFIG. 23 , a cell #11 (Cell#11) has the highest communication quality,and a cell #10 (Cell#10) has the lowest communication quality. The cellsdiagonally hatched in FIG. 23 are cells that cannot perform CoMP withthe serving cell.

In the CoMP measurement set, cells are ranked based on the RSRP/RSRQ ofthe CSI-RS by the UE being a communication quality. The CoMP measurementset is selected from the RRM measurement set. In this case, as disclosedin the first embodiment, cells are selected from only the cells in theCoMP cooperating set. This limits the CoMP measurement set to the cellscapable of CoMP. In the example shown in FIG. 23 , a cell #5 (Cell#5)has the highest communication quality and a cell #6 (Cell#6) has thelowest communication quality.

The ranking of the communication quality differs between the RRMmeasurement set and the CoMP measurement set because an indicator usedfor communication quality differs therebetween. This is because theRSRP/RSRQ of the CRS is used as the indicator of the communicationquality for the RRM measurement set, whereas the CSI-RS is used as theindicator of the communication quality for the CoMP measurement set.

As to the CoMP transmission points, the cells are ranked based on theCSI derived from the CSI-RS measurement value by the UE being acommunication quality. The CoMP transmission points are selected fromthe CoMP measurement set. In the example shown in FIG. 23 , the cell #5(Cell#5) has the highest communication quality and the cell #1 (Cell#1)has the lowest communication quality.

In the example shown in FIG. 23 , if the serving cell is switched basedon an RRM measurement report when the UE being subjected to CoMP hasmoved, the serving cell may be inadvertently switched to the cell thatcannot perform CoMP. For example, the cell #11 (Cell#11) becomes thecell having the best communication quality according to the RRMmeasurement report. In the case where the serving cell is switched suchthat the cell #11 (Cell#11) becomes a new serving cell, the new servingcell cannot perform CoMP, causing a problem that a good communicationquality cannot be obtained.

This embodiment will disclose the method for solving the above-mentionedproblem that a good communication quality cannot be obtained.

In switching of the serving cell performing CoMP, the cell capable ofCoMP is prioritized in selecting a new serving cell.

The serving cell performing CoMP is switched in the HO (including cellchange) process. The cell capable of CoMP is prioritized in selecting atarget cell in the HO decision process.

The cells in the CoMP cooperating set may be prioritized. In otherwords, the cells outside the CoMP cooperating set may be excluded.

The cells in the CoMP measurement set may be prioritized in selecting atarget cell in the HO decision process.

If the UE being subjected to CoMP moves, a new serving cell is the cellcapable of CoMP. This allows the UE to perform CoMP with the new servingcell, so that a good communication quality can be obtained.

For example, if the reception quality of the serving cell degrades andthe HO (including cell change) process is activated in FIG. 23 , not thecell #11 (Cell#11) that cannot perform CoMP but a cell #8 (Cell#8)capable of CoMP is selected in the selection of a target cell in the HOdecision process. This allows the UE to perform CoMP with a new servingcell, so that a good communication quality can be obtained.

As another example, if the reception quality of the serving celldegrades and the HO (including cell change) process is activated in FIG.23 , not the cell #11 (Cell#11) in the RRM measurement set but the cell#5(Cell#5) in the CoMP measurement set is selected in the selection of atarget cell in the HO decision process. This further improves thereception quality in the case where a new serving cell performs CoMP.

FIG. 24 is a diagram showing an exemplary sequence of a mobilecommunication system in a fifth embodiment. The sequence shown in FIG.24 is similar to the sequence shown in FIGS. 15 and 16 , and thus, thesame steps will be denoted by the same step numbers and commondescription will be omitted. FIG. 24 shows the sequence in a case wherethe cells capable of CoMP are prioritized in the selection of a targetcell in the HO decision process.

The serving cell having the central entity function performs the CoMPprocess on the UE1 as shown in Steps ST1501 to ST1526 and Step ST1530 ofFIGS. 15 and 16 .

In Step ST1526, the serving cell and the UE1 perform CoMPtransmission/reception and CSI feedback.

In Step ST2301, the UE1 performs RRM measurement through CRSmeasurement. In Step ST2302, the UE1 reports, to the serving cell, themeasurement results of the RRM measurement in Step ST2301 as ameasurement report message, according to the report condition. Themeasurement in Step ST2301 includes the CRS measurement of the servingcell per se. The measurement report in Step ST2302 includes the CRSmeasurement results of the serving cell per se.

In Step ST2303, the serving cell performs the HO decision process. TheHO decision process of Step ST2303 includes processes of Steps ST2304and ST2305.

In Step ST2304, the serving cell decides to perform the HO process onthe UE1 using the measurement report from the UE1. For example, if theCRS measurement results of the serving cell fall below a predeterminedthreshold, the serving cell decides to perform the HO process on theUE1.

In Step ST2305, the serving cell decides a target cell. The serving cellselects the cell having the best communication quality as a target cellamong the cells in the CoMP measurement set. The serving cell selects acell having the best communication quality in the CoMP measurement setfrom the CSI-RS measurement results by the UE being a HO target.

In Step ST2306, the serving cell that has performed the HO decisionprocess in Step ST2303 performs the HO process, with the cell selectedin Step ST2305 as a target cell.

Although as a new serving cell, the cell having the best CSI-RSreception quality in the CoMP measurement set is selected as a targetcell in the example shown in FIG. 24 , the cell having the best CSI-RSmeasurement results needs not to be selected. In other words, a targetcell may be selected also in consideration of other indicator, forexample, the load of each cell. The target cell may be anyin-CoMP-measurement-set cell.

If there is no cell to be prioritized, a conventional selection methodmay be used in the selection of a target cell in the HO decisionprocess. For example, in the case where only the measurement results ofthe cell #11 (Cell#11), the cell #12 (Cell#12), and the cell #13(Cell#13) are reported in the RRM measurement report of the UE, a targetcell may be selected from those cells.

This allows for switching of the serving cell such that a new servingcell keeps performing CoMP on the UE as long as possible to obtain agood reception quality, in the case where the UE being subjected to CoMPmoves and the reception quality of the serving cell degrades, requiringswitching of the serving cell.

Although the cells in the CoMP measurement set have been disclosed asthe cells capable of CoMP, the in-CoMP-active-set cells may beprioritized. Or, the in-CoMP-transmission-point cells may beprioritized.

The priority may be decided in the CoMP set. For example, the cells inthe CoMP transmission point may have the priority “1”, the cells in theCoMP active set may have the priority “2”, the cells in the CoMPmeasurement set may have the priority “3”, the cells in the CoMPoperation set may have the priority “4”, and the other cells may havethe priority “5”.

The selection of a new serving cell (target cell) in this manner allowsthe new serving cell to keep performing CoMP on a UE to become a targetto obtain a good reception quality as good as possible.

First Modification of Fifth Embodiment

Reference 5 discloses the use of the RRM measurement report for mobilitycontrol. This means that the RSRP/RSRQ measurement results of the CRS bythe UE are used for mobility control. If the RSRP/RSRQ measurementresults of the CRS by the UE are used for mobility control when the UEbeing subjected to CoMP moves, the following problem arises.

The problem arising in the case the RSRP/RSRQ measurement results of theCRS by the UE are used for mobility control will be described using anexample shown in FIG. 23 . Described below is the case where the UEbeing subjected to CoMP moves and then the serving cell is switchedbased on a conventional RRM measurement report.

In application of the method of selecting a target cell from the cellscapable of CoMP, disclosed in the fifth embodiment, the cell #8 (Cell#8)becomes the cell having the best communication quality according to theRRM measurement report. Thus, the serving cell is switched such that thecell #8(Cell#8) becomes a new serving cell.

In some cases, however, the cell #8 (Cell#8) in the CoMP measurement setdoes not become the cell having the best communication quality, andfurther, is not selected as a CoMP transmission point. In other words,the cell #8 (Cell#8) becomes the cell that does not perform CoMP datatransmission to the UE. The cell #8 (Cell#8) does not perform CoMP datatransmission/reception though it becomes a new serving cell. Thisincreases, for example, the number of cells other than the serving cellrelated to CoMP, whereby the serving cell cannot be switched to onesuitable for CoMP.

As described above, the cell having the best communication qualitythrough RRM measurement differs from the cell having the bestcommunication quality with the in-CoMP-measurement-set cell or the cellbeing a CoMP transmission point. This is because the CRS measurementresults present in the area to which the PDCCH is mapped are used forthe reception quality through RRM measurement, whereas the CSI-RSmeasurement results present in the area to which the PDSCH is mapped areused for the reception quality of the CoMP measurement set or the CoMPtransmission point. The data to be subjected to CoMP is mapped to thesymbols in the PDSCH area, meaning that the CRS measurement by theconventional RRM measurement does not correctly indicate the quality ofthe PDSCH during the execution of CoMP.

This modification will disclose the method for solving theabove-mentioned problem. In switching of the serving cell performingCoMP, the CSI-RS measurement results by the UE are used when a newserving cell is selected. The process of switching the serving cellperforming CoMP is performed in the HO (including cell change) process,and the CSI-RS measurement results are used when a target cell in the HOdecision process is selected. The CSI-RS measurement results may be theRSRP/RSRQ of the CSI-RS or the CSI (CSI feedback) derived from theCSI-RS measurement results.

For example, in FIG. 23 , if the HO (including cell change) process isactivated due to a reduction in the reception quality of the servingcell, not the cell #8 (Cell#8) having the best reception qualityaccording to the CRS measurement results but the cell #5 (Cell#5) havingthe best reception quality according to the CSI-RS measurement resultsis selected in the selection of a target cell in the HO decisionprocess. This allows the UE to obtain a good communication quality witha new serving cell.

The sequence in this modification may be obtained by changing a part ofthe sequence shown in FIG. 24 . That is, in this modification, in StepST2305 of FIG. 24 , the process of selecting a cell, which has the bestcommunication quality according to the measurement results, as a targetcell may be performed, from the CSI-RS measurement results by the UEbeing a HO target.

The cell in the CoMP measurement set or the cell in the CoMPtransmission point may be selected as the cell that has the bestreception quality according to the CSI-RS measurement results. When theUE being subjected to CoMP moves, a new serving cell becomes the cell inthe CoMP measurement set or the cell in the CoMP transmission points.This allows the UE to be subjected to CoMP including a new serving cell,so that a good communication quality can be obtained.

Second Modification of Fifth Embodiment

If the UE being subjected to CoMP moves, in some cases, the receptionquality of the serving cell degrades and the serving cell needs to beswitched. In the conventional process of switching a serving cell forthe UE not being subjected to CoMP, for example, in the HO process, theCRS measurement results of the serving cell by the UE are used toevaluate the reception quality of the serving cell.

As disclosed in the fifth embodiment and the first modification of thefifth embodiment, however, for the UE being subjected to CoMP, the CRSmeasurement results do not correctly indicate the communication qualityduring CoMP. Thus, for the UE being subjected to CoMP, if the receptionquality is judged to have degraded from the CRS measurement results ofthe serving cell and then the serving cell is switched as in theconventional case, in actuality, the communication quality during CoMPmay be good and there may be no need to switch the serving cell. In sucha case, a good communication quality may not be obtained with a newserving cell if the serving cell is switched.

This modification will disclose the method for solving theabove-mentioned problem. The CSI-RS measurement results of the servingcell by the UE are used when the serving cell performing CoMP is judgedto be switched. The CSI-RS measurement results by the UE are used as thereception quality of the serving cell. When the UE being subjected toCoMP moves, if the reception quality of the serving cell degrades, it isdecided to switch a serving cell. For example, it may be judged toswitch the serving cell if the reception quality of the serving cell isnot larger than a predetermined threshold. The CSI-RS measurementresults may be the RSRP/RSRQ of the CSI-RS or the CSI (CSI feedback)derived from the CSI-RS measurement results.

This solves such a problem that the serving cell is inadvertentlyswitched though the UE being subjected to CoMP has a good communicationquality with the serving cell. This allows the UE being subjected toCoMP to obtain a good communication quality with the serving cell.

Among the methods of handing a serving cell disclosed in the fourthembodiment, the method (2) or (3) may be used as the method of causingthe UE being subjected to CoMP to measure the CSI-RS of the servingcell. The UE measures the CSI-RS of the serving cell. The UE may measurethe CSI-RS of the serving cell regularly or periodically.

The serving cell may be switched in the HO (including cell change)process and the CSI-RS measurement results of the serving cell may beused in judging to perform HO in the HO decision process.

FIG. 25 is a diagram showing an exemplary sequence of a mobilecommunication system in the second modification of the fifth embodiment.The sequence shown in FIG. 25 is similar to the sequence shown in FIGS.15 and 16 and FIG. 24 , and thus, the same steps will be denoted by thesame step numbers and common description will be omitted. FIG. 25 showsthe sequence in the case where the CSI-RS measurement results of theserving cell are used in judging to perform HO in the HO decisionprocess. In this sequence, the process of Step ST2401 is performed inplace of the process of Step ST2304 of FIG. 24 .

The serving cell having the central entity function performs CoMP on theUE1, similarly to the processes of Steps ST1501 to ST1526 and ST1530 ofFIGS. 15 and 16 . In Step ST1515, the CSI-RS measurement report or CSIfeedback to be notified the serving cell from the UE may include theCSI-RS measurement results of the serving cell. Or, in Step ST1526, theCSI feedback to be notified the serving cell from the UE may include theCSI-RS measurement results of the serving cell. Or, the CSI-RS RSRP/RSRQmeasurement results of the serving cell may be notified together in StepST1526. This allows the serving cell to obtain the CSI-RS measurementresults of its own cell by the UE1.

In Step ST2400, the serving cell performs the HO decision process. TheHO decision process of Step ST2400 includes the processes of StepsST2401 and ST2305.

In Step ST2401, the serving cell decides to perform the HO process onthe UE1 using the CSI-RS measurement results from the UE1. For example,the serving cell decides to perform the HO process on the UE1 if theCSI-RS measurement results of the serving cell fall below apredetermined threshold.

In Step ST2305, the serving cell decides a target cell. In Step ST2306,the serving cell that has performed the HO decision process in StepST2400 performs the HO process with the cell selected in Step ST2305 asa target cell.

The method disclosed in this modification allows the UE being subjectedto CoMP to obtain a good communication quality with the serving cell.

This embodiment and the modifications thereof have disclosed that inswitching of the serving cell performing CoMP, the CSI-RS measurementresults by the UE are used to select a new serving cell and decide toperform HO.

For the use of the CSI-RS measurement results by the UE, the reportcondition for CSI-RS measurement may be newly provided. In place of theCRS measurement results being the report condition for the conventionalCRS measurement results, the CSI-RS measurement results may be used.

The serving cell notifies the UE of the report condition for CSI-RSmeasurement. Or, the serving cell may provide an indicator showing thatthe relevant measurement is used while CoMP is performed and then notifythe indicator. The serving cell may include at least any one of thereport condition and the indicator in the measurement configuration andthen notify the UE.

It may be statically decided that the measurement during CoMP is theCSI-RS measurement. For example, the measurement may be preliminarilydecided in, for example, specifications such that the UE and the networkcan share the recognition. This eliminates the need for the indicator,reducing the amount of information that requires signaling.

The cells on which CSI-RS measurement is performed by the UE may belimited to the cells notified of the CSI-RS configuration. It sufficesthat the serving cell also notifies the UE of the CSI-RS configurationof its own cell.

The CSI-RS configuration of the cell whose CSI-RS is to be measured isnotified the UE when the serving cell performs CoMP and, in this case,the relevant cells may be limited to the cells whose CSI-RS is to bemeasured. This may include the CSI-RS configuration of its own cell.

This allows the UE to recognize the CSI-RS configuration of the cell, sothat the UE can perform CSI-RS measurement.

The cells to be limited may be its own cell as well as the cell thatperforms additional RRM measurement, the cell in CoMP measurement set,and the cell in the CoMP active set.

The UE notifies the serving cell of the CSI-RS measurement results inaccordance with the CSI-RS report condition notified from the servingcell. This allows, in switching the serving cell for the UE beingsubjected to CoMP, the serving cell to use the CSI-RS measurementresults by the UE to select a new serving cell and decide to perform HO.

This embodiment has disclosed that in switching of the serving cellperforming CoMP, the CSI-RS measurement results by the UE are used toselect a new serving cell and decide to perform HO, but not limitedthereto, and the following four indicators (1) to (4) below may be used.

(1) Communication quality of uplink from UE. The uplink communicationquality may be the communication quality of the SRS, PUCCH, and PUSCH.

Location information of UE.

Measurement results on a downlink demodulation reference signal (DM-RS)by UE.

Mobility speed information of UE.

The use of the indicators (1) to (4) above allows the UE being subjectedto CoMP to switch the serving cell more suitable for CoMP, obtaining agood communication quality.

Sixth Embodiment

For CoMP and CA, an ePDCCH is studied as a new physical control channelin Release 11 of 3GPP (see R1-113157 (hereinafter, referred to as“Reference 6”) by 3GPP).

R1-114214 (hereinafter, referred to as “Reference 7”) by 3GPP disclosesthat the ePDCCH is multiplexed with the PDSCH on a symbol to which thePDSCH is mapped and that the ePDCCH can be mapped even in a subframefree from the PDCCH.

FIG. 26 is a diagram for describing the ePDCCH. FIG. 26 showsfrequency-time resources for one subframe. The vertical axis andhorizontal axis of FIG. 26 indicate the frequency and time,respectively. In FIG. 26 , the area represented by reference numeral“2501” indicates a symbol to which the PCFICH, PHICH, and PDCCH aremapped, and the area represented by reference numeral “2502” indicates asymbol to which the PDSCH is mapped. The area indicated by referencenumeral “2503” is the ePDCCH, which is multiplexed with the PDSCH on asymbol to which the PDSCH can be mapped.

As described above, the ePDCCH is mapped on a symbol to which the PDSCHcan be mapped, and thus, the UE fails to recognize whether or not theePDCCH has been mapped if no contrivance is made. Therefore, the UEcannot monitor the ePDCCH.

This embodiment will disclose the method of solving this problem. In theuse of the ePDCCH, the serving cell notifies the UE of the ePDCCHconfiguration through dedicated signaling. RRC signaling may be used asdedicated signaling.

In the use of the ePDCCH, the activation or deactivation of the ePDCCHis notified through MAC signaling. For example, the timing at which theUE starts or stops monitoring the ePDCCH is shown as the notification ofactivation or deactivation of the ePDCCH. The UE may start or stopmonitoring the ePDCCH upon receipt of the notification of activation ordeactivation of the ePDCCH. This reduces a delay time more beforestarting or stopping monitoring the ePDCCH than notifying the activationor deactivation through RRC signaling, whereby a change in surroundingradio wave environment can be supported.

As another method, the information on the activation or deactivation ofthe ePDCCH may be included in the DCI to be mapped to the PDCCH, andthen may be notified the UE. Or, the information on activation may beincluded in the DCI to be mapped to the PDCCH, and the information ondeactivation may be included in the DCI to be mapped to the ePDCCH, sothat the information is notified the UE. This allows for setting ofstarting or stopping monitoring of the ePDCCH in subframes. Therefore, achange in the surrounding radio wave environment for a shorter period oftime can be supported.

If the serving cell notifies the UE of the activation of the ePDCCHthrough MAC signaling, the UE starts monitoring the ePDCCH. If theserving cell notifies the UE of the deactivation of the ePDCCH throughMAC signaling, the UE stops monitoring the ePDCCH.

In the use of the ePDCCH for CoMP, the DCI of the ePDCCH to a target UEmay include the CoMP transmission point information. The informationsimilar to that in the case of the PDCCH may be included. The UE canrecognize CoMP transmission points by monitoring the ePDCCH.

If the ePDCCH is provided dedicatedly for the UE, the ePDCCH may be aCoMP target. This is possible when the serving cell preliminarilynotifies the in-CoMP-measurement-set cell or in-CoMP-active-set cell ofthe ePDCCH of the UE being a CoMP target. As disclosed in the embodimentbelow, the scheduling information of the UE being a CoMP target isnotified the in-CoMP-measurement-set cell or the in-CoMP-active-setcell. Thus, the use of the ePDCCH configuration information and thescheduling information of the UE allows each cell in the set to set theePDCCH of the UE as a CoMP target. The ePDCCH is also subjected to CoMP,so that the reception quality of the ePDCCH can be improved.

In the use of the ePDCCH, scheduling over the PDCCH may be avoided inthe subframe that is scheduled over the ePDCCH. The UE may avoidmonitoring the PDCCH in the subframe in which the ePDCCH is monitored.

In the use of the ePDCCH, the PDCCH may be used in notification ofpaging (paging indication (PI)). The UE monitors the PDCCH indiscontinuous reception cycles for receiving paging. If the ePDCCH ismapped in a subframe in which paging is notified, the UE monitors bothof the PDCCH and the ePDCCH. Examples of the uses of paging includenotification of an incoming call from the network, notification of achange in system information (SI), and notification of a public warningsystem (PWS) such as ETWS and CMAS. Thus, the UE can monitor both of thePDCCH and the ePDCCH to receive, for example, the notification of anincoming call from the network, notification of a change in systeminformation, and notification of the PWS while performing CoMP.

In the use of the ePDCCH, the PDCCH may be used in scheduling of thesystem information. The UE monitors the PDCCH at a reception timing forsystem information. In the case where the ePDCCH is mapped in thesubframe in which the system information is scheduled, the UE monitorsboth of the PDCCH and the ePDCCH. The UE can monitor both of the PDCCHand the ePDCCH to receive the system information while performing CoMP.

FIGS. 27 and 28 are diagrams showing an exemplary sequence of a mobilecommunication system in a sixth embodiment. FIGS. 27 and 28 arecontinuous with each other at a boundary BL2. FIGS. 27 and 28 show thesequence in the case where the ePDCCH is used.

In Step ST2601, the serving cell decides to use the ePDCCH for a targetUE (UE1) in cases of, for example, deciding to perform CoMP on the UE1and deciding to perform CA on the UE.

In Step ST2602, the serving cell decides the ePDCCH configuration forthe UE1. Examples of the parameters to be configured include theinformation indicative of physical resources to which the ePDCCH ismapped, the cycle in which the ePDCCH is mapped, the sequence specificto the UE to be used for the ePDCCH, and a monitoring mode. Theinformation indicative of physical resources to which the ePDCCH ismapped is, for example, a PRB number. The cycle in which the ePDCCH ismapped is, for example, the number of subframes, the number of radioframes, and the offsets of subframes. Examples of the monitoring modeinclude a mode in which the PDCCH and the ePDCCH are both monitored, amode in which the ePDCCH and at least any one of the PDCCH for pagingnotification and the PDCCH for system information scheduling aremonitored, and a mode in which only the ePDCCH is monitored, and thesemode types are made settable.

In Step ST2603, the serving cell notifies the UE1 of the ePDCCHconfiguration through RRC signaling.

In Step ST2604, the UE1 sets the received ePDCCH configuration.

In Step ST2605, the serving cell decides scheduling to the UE1 over theePDCCH.

In Step ST2606, the serving cell notifies the UF1 of the ePDCCHactivation of through MAC signaling.

In Step ST2607, the serving cell performs scheduling to the UE1 over theePDCCH.

In Step ST2608, the serving cell transmits the ePDCCH to the UE1 usingthe resources, cycle, and sequence configured in Step ST2602 in a symbolto which the PDSCH is mapped.

The UE1 notified of an ePDCCH activation signal in Step ST2606 startsmonitoring the ePDCCH.

In Step ST2609, the UE1 monitors the ePDCCH transmitted from the servingcell to obtain the scheduling information directed to its own UE.

In Step ST2610, the UE1 communicates with the serving cell based on thereceived scheduling information.

Next, the case where the use of the ePDCCH is stopped will be described.In Step ST2611, the serving cell decides not to use the ePDCCH for theUE1. In Step ST2612, the serving cell notifies the UE1 of ePDCCHdeactivation through MAC signaling. This notification is performed overthe ePDCCH.

In Step ST2613, the serving cell stops scheduling to the UE1 over theePDCCH and performs scheduling to the UE1 over the PDCCH.

In Step ST2616, the serving cell performs scheduling to the UE1 over thePDCCH.

In Step ST2614, the UE that has notified of an ePDCCH deactivationsignal in Step ST2612 stops monitoring the ePDCCH.

In Step ST2615, the UE1 starts monitoring the PDCCH transmitted from theserving cell to obtain the scheduling information directed to its ownUE.

In Step ST2617, the UE1 communicates with the serving cell based on thereceived scheduling information.

Next, the case where the serving cell decides not to use the ePDCCH forthe UE1 will be described. In Step ST2618, the serving cell decides notto use the ePDCCH for the UE1. For example, the serving cell decides notto use the ePDCCH in the case of, for example, stopping or havingstopped performing CoMP on the UE1 or stopping or having stopped CA onthe UE1.

In Step ST2619, the serving cell notifies the UE1 of an ePDCCHconfiguration release. The UE1 can recognize that the use of the ePDCCHhas been ended by receving the ePDCCH configuration release.

In Step ST2620, the serving cell that has notified the ePDCCHconfiguration release in Step ST2619 releases the ePDCCH configurationfor the UE1. Or, when being notified of a reception response to theprocess of Step ST2619 from the UE1, in Step ST2620, the serving cellmay release the ePDCCH configuration for the UE1. Thus, the physicalresources and sequence reserved for the UE1 can be released, allowingfor efficient use of resources.

In Step ST2621, the UE1 releases (resets) the set ePDCCH configuration.

The method disclosed in this embodiment allows the UE to recognizewhether or not the ePDCCH has been mapped and then monitor the ePDCCH.This allows for communication over the ePDCCH, which is effective in thecase where the ePDCCH is used in, for example, CoMP and CA.

Seventh Embodiment

A seventh embodiment will mainly disclose the signaling method and dataforwarding method between the serving cell and other cell different fromthe serving cell in the first embodiment. FIGS. 29, 30, and 31 arediagrams showing an exemplary sequence of a mobile communication systemin the seventh embodiment. FIGS. 29 and 30 are continuous with eachother at a boundary BL3. FIGS. 30 and 31 are continuous with each otherat a boundary BL4. The sequence shown in FIGS. 29 to 31 is similar tothe sequence shown in FIGS. 15 and 16 , and thus, the same steps will bedenoted by the same step numbers and common description will be omitted.FIGS. 29 to 31 show the case where the central entity is configured inthe serving cell, and thus, the central entity and the serving cell arenot particularly differentiated from each other and are referred to as aserving cell.

In Step ST7101, the serving cell requests the cell other than theserving cell of the cells included in the CoMP measurement set decidedin Step ST1530 to join the CoMP measurement set for the UE1. In thedescription below, the cell other than the serving cell of the cellsincluded in the CoMP measurement set may be merely referred to as a“CoMP measurement set cell”.

As a specific example, the serving cell notifies the CoMP measurementset cell of a CoMP measurement set request message. The following three(1) to (3) will be disclosed as specific examples of the informationshown in the CoMP measurement set request message.

(1) Joining the CoMP measurement set for the UE1 is requested.

Start of transmission of CSI-RS is requested.

Combination of (1) and (2) above.

In Step ST7102, the CoMP measurement set cell that has received, fromthe serving cell, the request to join the CoMP measurement set for theUE1 in Step ST7101 responds to the request to join the CoMP measurementset, to the serving cell. This response may be omitted. This reduces aload of the process to the response process. If it can join the CoMPmeasurement set for the UE1 or if it can start transmitting the CSI-RSto the UE1, the CoMP measurement set cell notifies the serving cell ofthis. Specifically, the CoMP measurement set cell notifies the servingcell of a CoMP measurement set request Ack message.

If it cannot join the CoMP measurement set for the UE1 or if it cannotstart transmitting the CSI-RS to the UE1, the CoMP measurement set cellnotifies the serving cell of this. Specifically, the CoMP measurementset cell notifies the serving cell of a CoMP measurement set requestNack message.

Specific examples of the indicator by which the CoMP measurement setcell judges that it cannot join the CoMP measurement set for the UE1 orit cannot start transmitting the CSI-RS to the UE1 include a high loadof the CoMP measurement set cell. This sequence will describe the casewhere the CoMP measurement set cell can join the CoMP measurement setfor the UE1.

In Step ST7103, the serving cell transmits the CSI-RS to the UE1.

In Step ST7104, the CoMP measurement set cell that has notified theserving cell that it can join the CoMP measurement set in Step ST7102starts transmitting the CSI-RS to the UE1.

In Step ST7105, the serving cell notifies the data directed to the UE1.Specifically, the serving cell notifies the CoMP data directed to theUE1.

The following three (1) to (3) will be disclosed as specific examples ofthe destination to be notified of the data by the serving cell.

(1) CoMP measurement set cell. In the case where the CoMP measurementset cell that has notified the data is not selected as a CoMPtransmission point, the CoMP measurement set cell discards the notifieddata. In this specific example (1), contrary to the specific example (3)below, data notification can be started to increase the time availablefor data notification irrespective of whether or not CoMP transmissionpoints are decided in Step ST1516. Data is notified at any timing aslong as it is after the serving cell decides to perform CoMP in StepST1508 and before CoMP transmission/reception is performed in StepST1519. There is ample time before the data notification timing,reducing a momentary high load.

(2) A cell other than the serving cell of the cells included in the CoMPactive set. In the description below, the cell other than the servingcell of the cells included in the CoMP active set may be merely referredto as a “CoMP active set cell”. If the CoMP active set cell that hasnotified the data is not selected as a CoMP transmission point, the CoMPactive set cell discards the notified data. Contrary to the specificexample (3) below, the specific example (2) can start data notificationto increase a time available for data notification irrespective ofwhether or not CoMP transmission points are decided in Step ST1516. Datais notified at any timing as long as it is after the serving celldecides to perform CoMP in Step ST1508 and before CoMPtransmission/reception is performed in Step ST1519. There is ample timebefore the data notification timing, reducing a momentary high load.

(3) A cell other than the serving cell of the cells included in the CoMPtransmission points. In the description below, the cell other than theserving cell of the cells included in the CoMP transmission points maybe merely referred to as a “CoMP transmission point”. Contrary to thespecific examples (1) and (2) above, in the specific example (3), thecell that is not selected as the CoMP transmission point will not benotified of data, so that the process of discarding data is notnecessary. This leads to an effect that an unnecessary process is notrequired. Data is notified at any timing as long as it is after theserving cell decides CoMP transmission points in Step ST1516 and beforeCoMP transmission/reception is performed in Step ST1519.

The following three (1) to (3) will be disclosed as specific examples ofthe types of data to be notified.

PDCP data unit, which may be PDCP PDU data or PDCP SDU data.

RLC data unit, which may be RLC PDU data or RLC SDU data.

MAC data unit, which may be MAC PDU data or MAC SDU data. Parametersrequired for data may be notified together depending on the types ofdata to be notified.

In Step ST7106, the serving cell notifies the CoMP transmission point ofscheduling information including the information indicative of the CoMPtransmission points decided in Step ST1516. In Step ST7106, thenecessary scheduling information may be notified depending on the typesof data notified in Step ST7105. Scheduling including the informationindicative of CoMP transmission points, or the scheduling informationbeing the scheduling results is referred to as “CoMP scheduling”.

After the process of Step ST7106, the processes of Steps ST1518 toST1529 are performed as in the first embodiment described above. FIG. 31shows the processes of Steps ST1519 and ST1526 more specifically.

Step ST1519 includes Steps ST2901 to ST2903. In Step ST2901, the UE1 andthe serving cell perform CoMP transmission/reception. In Step ST2902,the UE1 and the cell other than the serving cell included in the CoMPmeasurement set perform CoMP transmission/reception. In Step ST2903, theUE1 derives the CSI from the CSI-RS and then feeds back the CSI to theserving cell.

Step ST1526 includes Steps ST2904 to ST2906. The processes of StepsST2904 to ST2906 are performed similarly to the processes of StepsST2901 to ST2093.

FIG. 32 is a diagram showing another exemplary sequence of the mobilecommunication system in the seventh embodiment. The same steps of thesequence shown in FIG. 32 as those shown in the sequence shown in FIGS.15 and 16 will be denoted by the same step numbers, and commondescription will be omitted. FIG. 32 shows the sequence in the casewhere the central entity decides CoMP transmission points, where thecentral entity is differentiated from the serving cell. FIG. 32 showsanother specific example of the processes of Steps ST1515 to ST1518 ofFIGS. 29 to 31 .

In Step ST7201, the serving cell notifies the central entity of theCSI-RS measurement results received in Step ST1515. Specific examples ofthe CSI-RS measurement results include a CSI-RS measurement report andCSI feedback information.

In Step ST7202, the serving cell notifies the central entity of theinformation on the data to be subjected to CoMP (hereinafter, alsoreferred to as “data parameters”). Specific examples of the dataparameters include an amount of data and the quality of service (QoS)information. Or, the serving cell may notify the data to be subjected toCoMP as the data parameters.

In Step ST7204, the central entity performs adjustment between CoMPmeasurement sets for achieving CoMP of the data to be subjected to CoMPthat has been received in Step ST7202. Specifically, the central entityperforms adjustment as to whether or not the serving cell can accept thetransmission of the data. The serving cell performs scheduling to the UEthat is not a CoMP target, being served by the serving cell, whereby theadjustment allows for optimum scheduling.

In Step ST7205, the central entity performs adjustment between the CoMPmeasurement sets for achieving CoMP of the data to be subjected to CoMPthat has been received in Step ST7202. Specifically, the central entityperforms adjustment as to whether or not the CoMP measurement set cellcan accept the transmission of the data. The CoMP measurement set cellperforms scheduling to a UE that is not a CoMP target, being served bythe CoMP measurement set cell, whereby the adjustment allows for optimumscheduling. Adjustment may be performed between CoMP active sets.

In Step ST7203, the central entity performs scheduling for the UE1 basedon the information on the data to be subjected to CoMP that has beenreceived in Step ST7202, the results of the adjustment performed withthe serving cell in Step ST7204, and the results of the adjustmentperformed with the CoMP measurement set cell in Step ST7205.Specifically, the central entity decides CoMP transmission points. Thedetails of the process of Step ST7203 are similar to those of theprocess of Step ST1516 of FIGS. 15 and 16 .

After that, the central entity may perform adjustment again between theCoMP transmission points to decide the final CoMP scheduling.

In Step ST7207, the central entity notifies the serving cell of the CoMPscheduling decided in Step ST7203.

In Step ST7208, the serving cell notifies the CoMP measurement set cellof the scheduling received in Step ST7207. The central entity may notifythe CoMP measurement set cell of the scheduling decided in Step ST7203.

FIG. 33 is a diagram showing another exemplary sequence of the mobilecommunication system in the seventh embodiment. The same steps of thesequence shown in FIG. 33 as those of the sequence shown in FIGS. 15 and16 and FIG. 32 will be denoted by the same step numbers, and commondescription will be omitted. FIG. 33 shows the sequence when the servingcell and the central entity decide CoMP transmission points together,where the central entity is differentiated from the serving cell. FIG.33 shows another specific example of the processes of Steps ST1515 toST1518 of FIGS. 29 to 31 .

In Step ST7304, the serving cell decides scheduling, by its own cellalone, on the data to be subjected to CoMP for the UE1. The serving cellmay decide scheduling temporarily.

In Step ST7301, the serving cell notifies the central entity of arequest for adjustment between CoMP measurement sets. When notifying anadjustment request, the serving cell may notify the scheduling decidedin Step ST7304. Specific examples of scheduling include time-frequencyresources. The serving cell may notify a request for adjustment betweenCoMP active sets.

In Step ST7302, the central entity performs adjustment between the CoMPmeasurement sets for achieving scheduling that has been received in StepST7301. Specifically, the central entity performs adjustment as towhether or not the serving cell can accept the scheduling received inStep ST7301. The serving cell performs scheduling to the UE that is nota CoMP target, being served by the serving cell, whereby the adjustmentallows for optimum scheduling. The serving cell performs scheduling inStep ST7304, and thus, this step may be omitted assuming that theserving cell is capable of accepting scheduling.

In Step ST7303, the central entity performs adjustment between the CoMPmeasurement sets for achieving scheduling received in Step ST7301.Specifically, the central entity performs adjustment as to whether ornot the CoMP measurement set cell can accept the scheduling received inStep ST7301. The CoMP measurement set cell performs scheduling to the UEthat is not a CoMP target, being served by the CoMP measurement setcell, whereby the adjustment allows for optimum scheduling. The centralentity may perform adjustment between CoMP active sets.

In Step ST1516, the central entity performs CoMP scheduling for the UE1based on the scheduling received in Step ST7301, the results of theadjustment performed with the serving cell in Step ST7302, and theresults of the adjustment performed with the CoMP measurement set cellin Step ST7303. Specifically, the central entity decides CoMPtransmission points. The details of the process are similar to those ofthe process of Step ST1516 of FIGS. 15 and 16 .

Next disclosed is the case where a cell unified entity is newlyprovided. The cell unified entity is defined as the entity that hasappropriate functions of radio resource control (RRC), packet dataconvergence protocol (PDCP), radio link control (RLC), and medium accesscontrol (MAC) in a plurality of radio areas together. Hereinafter, inthe seventh embodiment, eighth embodiment, ninth embodiment, and tenthembodiment, the cell refers to the entity composed of all of thefunctions of the RRC, PDCP, RLC, MAC, and physical layer (PHY)constituting one radio area. Also, a sub cell refers to the entitycomposed of part of the functions of the RRC, PDCP, RLC, MAC, and PHYconstituting one radio area.

The cell and sub cell having the PHY function have the function ofbroadcasting broadcast information. They may have the function ofbroadcasting an identifier identifiable by the UE.

FIG. 34 is a block diagram for describing a specific example of the cellunified entity. A cell unified entity 7416 is connected to a first subcell 7401, a second sub cell 7406, and a third sub cell 7411.

The first sub cell 7401 defines one radio area and includes a MAC 7402and a PHY 7403. The PHY 7403 includes a baseband unit (BB) 7404 and aradio frequency unit (RF) 7405.

The second sub cell 7406 defines one radio area and includes a MAC 7407and a PHY 7408. The PHY 7408 includes a BB 7409 and an RF 7410.

The third sub cell 7411 defines one radio area and includes a MAC 7412and a PHY 7413. The PHY 7413 includes a BB 7414 and an RF 7415.

The cell unified entity 7416 has the functions of the RRC 7417, the PDCP7418, and the RLC 7419 in the radio area defined by the first sub cell7401, the radio area defined by the second sub cell 7406, and the radioarea defined by the third sub cell 7412 together. In the descriptionbelow, the cell unified entity that has the functions of the RRC, PDCP,and RLC in a plurality of radio areas together, such as the cell unifiedentity 7416, may also be referred to as a “first cell unified entity”.

FIG. 35 is a block diagram for describing a specific example of anothercell unified entity. A cell unified entity 7513 is connected to a fourthsub cell 7501, a fifth sub cell 7505, and a sixth sub cell 7509.

The fourth sub cell 7501 defines one radio area and includes a PHY 7502.The PHY 7502 includes a BB 7503 and an RF 7504.

The fifth sub cell 7505 defines one radio area and includes a PHY 7506.The PHY 7506 includes a BB 7507 and an RF 7508.

The sixth sub cell 7509 defines one radio area and includes a PHY 7510.The PHY 7510 includes a BB 7511 and an RF 7512.

The cell unified entity 7513 has the functions of the RRC 7514, the PDCP7515, the RLC 7516, and the MAC 7517 in the radio area defined by thefourth sub cell 7501, the radio area defined by the fifth sub cell 7505,and the radio area defined by the sixth sub cell 7509 together. In thedescription below, the cell unified entity that has the functions of theRRC, PDCP, RLC, and MAC in a plurality of radio areas together, such asthe cell unified entity 7513, may also be referred to as a “second cellunified entity”.

As another specific example, a cell unified entity, which has thefunctions of the RRC, the functions of the PDCP, the functions of theRLC, and at least the scheduling function of the functions of the MAC ina plurality of radio areas together, is conceivable. This cell unifiedentity may also be referred to as a “third cell unified entity”.

FIGS. 36, 37, and 38 are diagrams showing another exemplary sequence ofthe mobile communication system in the seventh embodiment. FIGS. 36 and37 are continuous with each other at a boundary BL5. FIGS. 37 and 38 arecontinuous with each other at a boundary BL6. The sequence shown inFIGS. 36 to 38 is similar to the sequence shown in FIGS. 15 and 16 , andthus, the same steps will be denoted by the same step numbers and commondescription will be omitted. FIGS. 36 to 38 show the sequence when CoMPin a case where the first cell unified entity including the RRC 7417,the PDCP 7418, and the RLC 7419 is differentiated from the sub cell.This sequence shows the case where the central entity is configured inthe serving sub cell, and thus, the central entity and the serving subcell are not particularly differentiated from each other and arereferred to as a serving cell.

In Step ST7601, the first cell unified entity sets an RRM measurementconfiguration. The details of the process of Step ST7601 are similar tothose of the process of Step ST1501 of FIGS. 15 and 16 .

In Step ST7602, the first cell unified entity notifies the serving subcell of the RRM measurement configuration set in Step ST7601.

In Step ST7603, the serving sub cell notifies the UE1 of the RRMmeasurement configuration received in Step ST7602. The details of theprocess of Step ST7603 are similar to those of the process of StepST1502 of FIGS. 15 and 16 .

In Step ST7604, the UE1 reports the CRS measurement results to theserving sub cell. The details of the process of Step ST7604 are similarto those of the process of Step ST1504 of FIGS. 15 and 16 .

In Step ST7605, the serving sub cell notifies the first cell unifiedentity of the report of the measurement results received in Step ST7604.

In Step ST7606, the first cell unified entity creates an RRM measurementset. The details of the process of Step ST7606 are similar to those ofthe process of Step ST1505 of FIGS. 15 and 16 .

In Step ST7607, the first cell unified entity notifies the serving subcell of the data. Specifically, the first cell unified entity notifiesthe data directed to the UE1. Specific examples of the types of data tobe notified include an RLC data unit. The data to be notified may be RLCPDU data. The first cell unified entity may notify the parametersrequired for the data together. Specific examples of the parametersrequired include the parameters required for the MAC process of theserving sub cell.

In Step ST7608, the serving sub cell performs scheduling of the datareceived in Step ST7607. The serving sub cell may perform MACscheduling.

In Step ST7609, the UE1 and the serving sub cell communicate data in atleast any one of downlink (DL) and uplink (UL).

In Step ST7610, the serving sub cell communicates data with the firstcell unified entity for the DL data to be transmitted to the UE1 and theUL data received from the UE1. The data to be notified is processedsimilarly to the process of Step ST7607.

In Step ST7611, the UE1 feeds back the CQI derived from the CRS to theserving sub cell.

In Step ST7612, the serving sub cell notifies the first cell unifiedentity of the CQI feedback data received in Step ST7611.

In Step ST7613, the first cell unified entity decides whether or not toperform CoMP. The details of the process of Step ST7613 are similar tothose of the process of Step ST1508 of FIGS. 15 and 16 .

In Step ST7638, the first cell unified entity selects and decides a CoMPmeasurement set. The details of the process of Step ST7638 are similarto those of the process of Step ST1530 of FIGS. 15 and 16 .

If the first cell unified entity can recognize, for example, the loadcondition of the sub cell included in the CoMP measurement set to judgewhether or not the CoMP measurement set sub cell can join the CoMPmeasurement set for the UE1, the processes corresponding to Steps ST7101and ST7102 of FIGS. 29 to 31 can be omitted. The first cell unifiedentity is provided in the mobile communication system that supports CoMPin this manner, preventing a control delay.

In Step ST7614, the first cell unified entity requests the serving subcell to start transmitting the CSI-RS.

In Step ST7615, the first cell unified entity requests the cell or thesub cell other than the serving sub cell of the cells included in theCoMP measurement set to start transmitting the CSI-RS. In thedescription below, the cell or the sub cell other than the serving subcell among the sub cells included in the CoMP measurement set may bealso referred to as a “CoMP measurement set sub cell”.

In Step ST7616, the first cell unified entity sets the CoMP measurementconfiguration for the UE1. The details of the process of Step ST7616 aresimilar to those of the process of Step ST1509 of FIGS. 15 and 16 .

In Step ST7617, the first cell unified entity notifies the serving subcell of the CoMP measurement configuration for the UE1 set in StepST7616.

In Step ST7618, the serving sub cell notifies the UE1 of the CoMPmeasurement configuration received in Step ST7617. The details of theprocess of Step ST7618 are similar to those of the process of StepST1510 of FIGS. 15 and 16 .

In Step ST7619, the serving sub cell transmits the CSI-RS to the UE1.The serving sub cell may start transmitting the CSI-RS upon receipt of arequest to start transmitting the CSI-RS from the first cell unifiedentity in Step ST7614. This allows the serving sub cell to transmitCSI-RS only in the case where the user equipment being served by theserving sub cell performs measurement using the CSI-RS, reducing thepower consumption of the serving sub cell.

In Step ST7620, the CoMP measurement set sub cell transmits the CSI-RSto the UE1. The CoMP measurement set sub cell may start transmitting theCSI-RS upon receipt of a request to start transmitting the CSI-RS fromthe first cell unified entity in Step ST7615. This allows the CoMPmeasurement set sub cell to transmit the CSI-RS only in the case wherethe user equipment being served by the CoMP measurement set sub cellperforms measurement using the CSI-RS, reducing the power consumption ofthe CoMP measurement set sub cell.

In Step ST7621, the UE1 reports the CSI-RS measurement results to theserving sub cell. The details of the process of Step ST7621 are similarto those of the process of Step ST1515 of FIGS. 15 and 16 .

In Step ST7622, the first cell unified entity notifies the serving subcell of the data. The details of the process of Step ST7622 are similarto those of the process of Step ST7607.

In Step ST7623, the serving sub cell decides CoMP transmission points.The details of the process of deciding CoMP transmission points aresimilar to those of the process of Step ST1516 shown in FIG. 16 .

In Step ST7625, the serving sub cell notifies the CoMP measurement setsub cell of the data directed to the UE1. Specifically, the serving subcell notifies the data for CoMP directed to the UE1.

Specific examples of the types of data to be notified include a MAC dataunit, MAC PDU data, and MAC SDU data.

Or, the first cell unified entity may notify the CoMP measurement setsub cell of the data directed to the UE1. Specifically, the first cellunified entity notifies the data for CoMP directed to the UE1. Thefollowing three (1) to (3) will be disclosed as specific examples of thetypes of data to be notified.

PDCP data unit, which may be PDCP PDU data or PDCP SDU data.

RLC data unit, which may be RLC PDU data or RLC SDU data.

MAC data unit, which may be MAC PDU data or MAC SDU data. For MAC dataunit, the first cell unified entity may obtain the MAC data unitrequired from the serving sub cell.

The parameters required for the data at each layer may be notifiedtogether. As a specific example of the parameters, in the case where (1)the PDCP data unit is notified, the parameters required for the RLCprocess and the parameters required for the MAC process are notified.Meanwhile, in the case where (2) the RLC data unit is notified, theparameters required for the MAC process are notified.

The following two (1) and (2) will be disclosed as specific examples ofthe cell notified the data directed to the UE1 by the serving sub cell.

(1) The serving sub cell notifies the CoMP transmission sub cell decidedin Step ST7623 of the data directed to the UE1. In this case, thenotification of the unnecessary data to the CoMP transmission sub cellcan be reduced compared with the specific example (2) described below,though the cell is a CoMP measurement set sub cell.

(2) The serving sub cell notifies the CoMP measurement set sub cell ofthe data directed to the UE1. In this case, there is no need to wait thedecision of CoMP transmission sub cell in Step ST7623 for datanotification. Thus, the serving sub cell notifies the CoMP measurementset sub cell of the data directed to the UE1 at any timing as long as itis after the decision of a CoMP measurement set in Step ST7638 andbefore the notification of scheduling of Step ST7626. The first cellunified entity may notify the serving sub cell of the decided CoMPmeasurement set. It suffices to discard the data directed to the UE1 inthe CoMP measurement set sub cells that have not been selected as theCoMP transmission sub cell. In this case, compared with the specificexample (1), there is ample time before the data notification timing,reducing a momentary high load.

In Step ST7626, the serving sub cell may notify the CoMP transmissionsub cell of CoMP scheduling including the information indicative of theCoMP transmission points decided in Step ST7623. The serving sub cellmay notify the CoMP measurement set sub cell via the first cell unifiedentity.

In Step ST7627, the serving sub cell performs CoMP scheduling includingthe information on the CoMP transmission points decided in Step ST7623,and then notifies the UE1. The details of the process of Step ST7627 aresimilar to those of the process of Step ST1518 of FIGS. 15 and 16 .

In Steps ST7628 and ST7629, the UE1, the serving sub cell, and the CoMPtransmission sub cell perform CoMP transmission/reception.

In Step ST7630, the UE1 derives the CSI from the CSI-RS and then feedsback the CSI to the serving sub cell.

In Step ST7631, the UE1 reports the CRS measurement results to theserving sub cell. The details of the process of Step ST7631 are similarto those of the process of Step ST1504 of FIGS. 15 and 16 .

In Step ST7632, the serving sub cell notifies the first cell unifiedentity of the report of the CRS measurement results received in StepST7631.

In Step ST7633, the first cell unified entity that has received themeasurement report in Step ST7632 changes an RRM measurement set asrequired. The details of the process of Step ST7633 are similar to thoseof the process of Step ST1524 of FIGS. 15 and 16 .

In Step ST7634, the first cell unified entity judges whether or not tochange the CoMP measurement set. The details of the process of StepST7634 are similar to those of the process of FIGS. 15 and 16 . Ifjudging to change the CoMP measurement set in Step ST7634, the firstcell unified entity changes the cells in the CoMP measurement set andreturns to the process of Step ST7614. If judging not to change the CoMPmeasurement set in Step ST7634, the first cell unified entity moves toStep ST7635.

In Step ST7635, the first cell unified entity decides to release CoMP,namely, stop performing CoMP.

In Step ST7636, the first cell unified entity notifies the serving subcell of the release of the CoMP measurement configuration of the UE1.

In Step ST7637, the serving sub cell notifies the UE1 of the release ofthe CoMP measurement configuration of the UE1 that has been received inStep ST7636. The details of the process of Step ST7637 are similar tothose of the process of Step ST1528 of FIGS. 15 and 16 .

FIG. 39 is a diagram showing another exemplary sequence of the mobilecommunication system in the seventh embodiment. The same steps of thesequence shown in FIG. 39 as those of the sequence shown in FIG. 38 willbe denoted by the same step numbers, and common description will beomitted. FIG. 39 shows the sequence when the central entity decides CoMPtransmission points, where the central entity is differentiated from theserving sub cell. FIG. 39 shows another specific example of theprocesses of Steps ST7621 to ST7627 of FIGS. 36 to 38 .

In Step ST7701, the serving sub cell notifies the central entity of theCSI-RS measurement results received in Step ST7621. Specific examples ofthe CSI-RS measurement results include a CSI-RS measurement report andCSI feedback information.

In Step ST7702, the first cell unified entity notifies the centralentity of data. The details of the process of Step ST7702 are similar tothose of the process of Step ST7607 of FIGS. 36 to 38 .

In Step ST7704, the central entity performs adjustment between CoMPmeasurement sets for achieving CoMP of the data to be subjected to CoMPthat has been received in Step ST7702. Specifically, the central entityperforms adjustment as to whether or not the serving sub cell can acceptthe transmission of the data. The serving sub cell performs schedulingto the UE that is not a CoMP target, being served by the serving subcell, whereby the adjustment allows for optimum scheduling.

In Step ST7705, the central entity performs adjustment between the CoMPmeasurement sets for achieving CoMP of the data to be subjected to CoMPthat has been received in Step ST7702. Specifically, the central entityperforms adjustment as to whether or not the CoMP measurement set subcell can accept the transmission of the data. The CoMP measurement setsub cell performs scheduling to the UE that is not a CoMP target, beingserved by the CoMP measurement set sub cell, whereby the adjustmentallows for optimum scheduling. The CoMP measurement set sub cell mayperform adjustment between CoMP active sets.

In Step ST7703, the central entity performs scheduling for the UE1 basedon the information on the data to be subjected to CoMP that has beenreceived in Step ST7702, the results of the adjustment performed withthe serving sub cell in Step ST7704, and the results of the adjustmentperformed with the CoMP measurement set sub cell in Step ST7705.Specifically, the central entity decides CoMP transmission points. Thedetails of the process of Step ST7703 are similar to those of theprocess of Step ST1516 of FIGS. 15 and 16 .

After that, the central entity may perform adjustment again between theCoMP transmission points to decide the final CoMP scheduling.

In Step ST7707, the central entity notifies the serving sub cell and theCoMP measurement set sub cell of the data directed to the UE1.Specifically, the central entity notifies the data for CoMP directed tothe UE1.

In Step ST7708, the central entity notifies the serving sub cell of CoMPscheduling including the information indicative of the CoMP transmissionpoints decided in Step ST7703. The central entity may notify the servingsub cell of CoMP scheduling including the information indicative of theCoMP transmission points decided in Step ST7703 via the first cellunified entity.

In Step ST7709, the central entity notifies the CoMP measurement set subcell of the CoMP scheduling including the information indicative of theCoMP transmission points decided in Step ST7703. The central entity maynotify the CoMP measurement set sub cell via the first cell unifiedentity.

FIG. 40 is a diagram showing another exemplary sequence of the mobilecommunication system in the seventh embodiment. The same steps of thesequence shown in FIG. 40 as those of the sequence shown in FIGS. 36 to39 will be denoted by the same step numbers, and common description willbe omitted. FIG. 40 shows the sequence when the serving sub cell and thecentral entity decide CoMP transmission points together, where thecentral entity is differentiated from the serving sub cell. FIG. 40shows another specific example of the processes of Steps ST7621 toST7627 of FIGS. 36 to 38 .

In Step ST7801, the serving sub cell decides scheduling, by its own cellalone, on the data to be subjected to CoMP for the UE1. The serving subcell may temporarily decide scheduling.

In Step ST7802, the serving sub cell notifies the central entity of arequest for adjustment between CoMP measurement sets. When notifying anadjustment request, the serving sub cell may notify the schedulingdecided in Step ST7801. Specific examples of scheduling includetime-frequency resources. The serving sub cell may notify a request foradjustment between CoMP active sets.

In Step ST7803, the central entity performs adjustment between the CoMPmeasurement sets for achieving scheduling that has been received in StepST7802. Specifically, the central entity performs adjustment as towhether or not the serving sub cell can accept the scheduling receivedin Step ST7802. The serving sub cell performs scheduling to the UE thatis not a CoMP target, being served by the serving sub cell, and thus,the adjustment allows for optimum scheduling. The serving sub cellperforms scheduling in Step ST7801, whereby the serving sub cell mayjudge that the central entity can accept the scheduling and omit thisstep.

In Step ST7804, the central entity performs adjustment between the CoMPmeasurement sets for achieving the scheduling that has been received inStep ST7802. Specifically, the central entity performs adjustment as towhether or not the CoMP measurement set sub cell can accept thescheduling received in Step ST7802. The CoMP measurement set sub cellperforms scheduling to the UE that is not a CoMP target, being served bythe CoMP measurement set sub cell, and thus, the adjustment allows foroptimum scheduling. The central entity may perform adjustment betweenCoMP active sets.

In Step ST7805, the central entity performs CoMP scheduling for the UE1based on the scheduling received in Step ST7802, the results of theadjustment performed with the serving sub cell in Step ST7803, and theresults of the adjustment performed with the CoMP measurement set subcell in Step ST7804. Specifically, the central entity decides CoMPtransmission points. The details of the process are similar to those ofthe process of Step ST1516 of FIGS. 15 and 16 .

The first cell unified entity may have the function of the centralentity. Or, the central entity may have the function of the first cellunified entity. Or, the same entity may have the function of the centralentity and the function of the first cell unified entity. Thiseliminates the need for signaling and communication between the firstcell unified entity and the central entity, preventing a control delay.Specifically, for example, the process of Step ST7702 of FIG. 39 can beomitted.

FIG. 41 to FIG. 43 are diagrams showing another exemplary sequence ofthe mobile communication system in the seventh embodiment. FIGS. 41 and42 are continuous with each other at a boundary BL7. FIGS. 42 and 43 arecontinuous with each other at a boundary BL8. The sequence shown inFIGS. 41 to 43 is similar to the sequences shown in FIGS. 15 and 16 andFIGS. 36 to 38 , and thus, the same steps will be denoted by the samestep numbers and common description will be omitted. FIG. 41 to FIG. 43show the sequence of performing CoMP in the case where a sub cell isdifferentiated from a second cell unified entity including an RRC 7514,a PDCP 7515, an RLC 7516, and a MAC 7517. This sequence shows the casewhere the central entity is configured in the second cell unifiedentity, and thus, the central entity and the second cell unified entityare not particularly differentiated from each other and are referred toas a second cell unified entity. The same holds true for the case wherethe central entity is configured in a third cell unified entity.

In Step ST7901, the second cell unified entity sets an RRM measurementconfiguration. The details of the process of Step ST7901 are similar tothose of the process of Step ST1501 of FIGS. 15 and 16 .

In Step ST7902, the second cell unified entity notifies the serving subcell of the RRM measurement configuration set in Step ST7901.

In Step ST7903, the serving sub cell notifies the second cell unifiedentity of the report of the measurement results received in Step ST7604.

In Step ST7904, the second cell unified entity creates an RRMmeasurement set. The details of the process of Step ST7904 are similarto those of the process of Step ST1505 of FIGS. 15 and 16 .

In Step ST7905, the second cell unified entity notifies the serving subcell of data. Specifically, the second cell unified entity notifies thedata directed to the UE1. Specific examples of the types of data to benotified include a MAC data unit. The data to be notified may be MAC PDUdata or MAC SDU data. The parameters required for the data may benotified together.

In Step ST7906, the second cell unified entity performs data scheduling.The second cell unified entity may perform MAC scheduling.

In Step ST7907, the second cell unified entity notifies the serving subcell of the scheduling performed in Step ST7906.

In Step ST7908, the serving sub cell notifies the second cell unifiedentity of the CQI feedback data received in Step ST7611.

In Step ST7909, the second cell unified entity decides whether or not toperform CoMP. The details of the process of Step ST7909 are similar tothose of the process of Step ST1508 of FIGS. 15 and 16 .

In Step ST7926, the second cell unified entity selects and decides aCoMP measurement set. The details of the process of Step ST7926 aresimilar to those of the process of Step ST1530 of FIGS. 15 and 16 .

If the second cell unified entity can recognize the load condition ofthe sub cell included in the CoMP measurement set to judge whether ornot the CoMP measurement set sub cell can join the CoMP measurement setfor the UE1, the processes equivalent to Steps ST7101 and ST7102 ofFIGS. 29 to 31 can be omitted. The second cell unified entity isprovided in the mobile communication system that supports CoMP in thismanner, preventing a control delay.

In Step ST7910, the second cell unified entity requests the serving subcell to start transmitting the CSI-RS.

In Step ST7911, the second cell unified entity requests the CoMPmeasurement set sub cell to start transmitting the CSI-RS.

In Step ST7912, the second cell unified entity sets the CoMP measurementconfiguration for the UE1. The details of the process of Step ST7912 aresimilar to those of the process of Step ST1509 of FIGS. 15 and 16 .

In Step ST7913, the second cell unified entity notifies the serving subcell of the CoMP measurement configuration for the UE1 set in StepST7912.

In Step ST7914, the serving sub cell transmits the CSI-RS to the UE1.The serving sub cell may receive a request to start transmitting theCSI-RS from the second cell unified entity in Step ST7910 to starttransmitting the CSI-RS. This allows the serving sub cell to transmitthe CSI-RS only in the case where a user equipment being served by theserving sub cell performs measurement using the CSI-RS, reducing thepower consumption of the serving sub cell.

In Step ST7915, the CoMP measurement set sub cell transmits the CSI-RSto the UE1. The CoMP measurement set sub cell may start transmitting theCSI-RS upon receipt of a request to start transmitting the CSI-RS fromthe second cell unified entity in Step ST7911. This allows the CoMPmeasurement set sub cell to transmit the CSI-RS only in the case where auser equipment being served by the CoMP measurement set sub cellperforms measurement using the CSI-RS, reducing the power consumption ofthe sub cell included in the CoMP measurement set.

In Step ST7916, the serving sub cell notifies the second cell unifiedentity of the CSI-RS measurement results received in Step ST7621.

In Step ST7917, the second cell unified entity decides CoMP transmissionpoints. The details of the process of deciding CoMP transmission pointsare similar to those of the process of Step ST1516 shown in FIG. 16 .

In Step ST7918, the second cell unified entity notifies the serving subcell and the CoMP measurement set sub cell of the data directed to theUE1. Specifically, the second cell unified entity notifies the data forCoMP directed to the UE1.

The following three (1) to (3) will be disclosed as specific examples ofthe types of data to be notified.

PDCP data unit, which may be PDCP PDU data or PDCP SDU data.

RLC data unit, which may be RLC PDU data or RLC SDU data.

MAC data unit, which may be MAC PDU data or MAC SDU data.

The parameters required for the data at each layer may be notifiedtogether. As specific examples of the parameters, the parametersrequired for the RLC process and the parameters required for the MACprocess are notified in the case where (1) the PDCP data unit isnotified, or the parameters required for the MAC process are notified inthe case where (2) the RLC data unit is notified.

A specific example of the cell notified of the data directed to the UE1by the second cell unified entity is similar to that of the first cellunified entity of FIGS. 36 to 38 , which will not be described here.

In Step ST7919, the second cell unified entity notifies the serving subcell and the CoMP measurement set sub cell of CoMP scheduling includingthe information indicative of the CoMP transmission points decided inStep ST7917. Or, the second cell unified entity may notify the CoMPtransmission sub cell and the CoMP active set sub cell of CoMPscheduling.

In Step ST7920, the serving sub cell notifies the second cell unifiedentity of the CSI feedback data received in Step ST7630.

In Step ST7921, the serving sub cell notifies the second cell unifiedentity of the report of the measurement results received in Step ST7631.

In Step ST7922, the second cell unified entity that has received themeasurement report in Step ST7921 changes the RRM measurement set asrequired. The details of the process of Step ST7922 are similar to thoseof the process of Step ST1524 of FIGS. 15 and 16 .

In Step ST7923, the second cell unified entity judges whether or not tochange the CoMP measurement set. The details of the process of StepST7923 are similar to those of the process of Step ST1525 of FIGS. 15and 16 . If judging to change the CoMP measurement set in Step ST7923,the second cell unified entity changes the cells in the CoMP measurementset and returns to the process of Step ST7910. If judging not to changethe CoMP measurement set in Step ST7923, the second cell unified entitymoves to Step ST7924.

In Step ST7924, the second cell unified entity decides to release CoMP,namely, stop performing CoMP.

In Step ST7925, the second cell unified entity notifies the serving subcell of the release of the CoMP measurement configuration for the UE1.

FIG. 44 is a diagram showing another exemplary sequence of the mobilecommunication system in the seventh embodiment. The same steps of thesequence shown in FIG. 44 as those of the sequence shown in FIGS. 36 to39 and FIGS. 41 to 43 will be denoted by the same step numbers, andcommon description will be omitted. FIG. 44 shows the sequence when thecentral entity decides CoMP transmission points, where the centralentity is differentiated from the second cell unified entity. FIG. 44shows another specific example of the processes of Steps ST7621 toST7627 of FIG. 41 to FIG. 43 . The same holds true for the case wherethe central entity is differentiated from the third cell unified entity.

In Step ST8001, the second cell unified entity notifies the centralentity of the information on the data to be subjected to CoMP(hereinafter, also referred to as “data parameters”). Specific examplesof the data parameters include an amount of data and service QoSinformation. The second cell unified entity may notify the centralentity of the data to be subjected to CoMP.

In Step ST8002, the central entity performs adjustment between CoMPmeasurement sets for achieving CoMP of the data to be subjected to CoMPreceived in Step ST8001. The central entity may perform adjustmentbetween CoMP active sets. Specifically, the central entity performs,with the second cell unified entity, adjustment as to whether or not theserving sub cell and the CoMP measurement set sub cell can accept thedata transmission. The second cell unified entity performs scheduling tothe UE that is not a CoMP target, being served by the serving sub cell,and scheduling to the UE that is not a CoMP target, being served by theCoMP measurement set sub cell, whereby the adjustment allows for optimumscheduling. Adjustment with each sub cell is not required but collectiveadjustment with the second cell unified entity is only required, andthus, a control delay can be prevented by providing the second cellunified entity in the mobile communication system that supports CoMP.

In Step ST7703, the central entity decides CoMP scheduling. The centralentity performs CoMP scheduling for the UE1 based on the information onthe data to be subjected to CoMP that has been received in Step ST8001and the results of the adjustment performed with the second cell unifiedentity in Step ST8002. Specifically, the central entity decides CoMPtransmission points. The details of the process of Step ST7703 aresimilar to those of the processes of Step ST1516 of the sequence shownin FIGS. 15 and 16 .

After that, the central entity may perform adjustment again between theCoMP transmission points to decide the final CoMP scheduling.

In Step ST8004, the central entity notifies the second cell unifiedentity of the CoMP scheduling decided in Step ST7703.

In Step ST8005, the second cell unified entity notifies the serving subcell of the scheduling received in Step ST8004. The central entity maynotify the serving sub cell of the scheduling decided in Step ST7703.

In Step ST8006, the second cell unified entity notifies the CoMPmeasurement set sub cell of the CoMP scheduling received in Step ST8004.The central entity may notify the CoMP measurement set sub cell of theCoMP scheduling decided in Step ST7703.

FIG. 45 is a diagram showing another exemplary sequence of the mobilecommunication system in the seventh embodiment. The same steps of thesequence shown in FIG. 45 as those of the sequences shown in FIGS. 36 to39 and FIGS. 41 to 43 will be denoted by the same step numbers, andcommon description will be omitted. FIG. 45 shows the sequence when thesecond cell unified entity and the central entity decide CoMPtransmission points together, where the central entity is differentiatedfrom the second cell unified entity. FIG. 45 shows another specificexample of the processes of Steps ST7621 to ST7627 of FIG. 41 to FIG. 43. The same holds true for the case where the central entity isdifferentiated from the third cell unified entity.

In Step ST8101, the serving sub cell notifies the second cell unifiedentity of the CSI-RS measurement results received in Step ST7601.Specific examples of the CSI-RS measurement results include CSI-RSmeasurement report and CSI feedback information.

In Step ST8102, the second cell unified entity decides scheduling, byits own cell alone, for the UE1. The decision may be made temporalily.

In Step ST8103, the second cell unified entity notifies the centralentity of a request to perform adjustment between CoMP measurement sets.When notifying an adjustment request, the second cell unified entity maynotify the scheduling decided in Step ST8102. Specific examples ofscheduling include time-frequency resources. The second cell unifiedentity may request an adjustment between CoMP active sets.

The second cell unified entity may have the function of the centralentity. Or, the central entity may have the function of the second cellunified entity. Or, the same entity may have the function of the centralentity and the function of the second cell unified entity. FIGS. 41 to43 show this example.

Alternatively, the third cell unified entity may have the function ofthe central entity. Or, the central entity may have the function of thethird cell unified entity. Or, the same entity may have the function ofthe central entity and the function of the third cell unified entity.FIGS. 41 to 43 show this example.

This does not require the signaling and communication between the secondcell unified entity and the central entity, preventing a control delay.Or, the signaling and communication between the third cell unifiedentity and the central entity are not necessary, preventing a controldelay.

Specifically, for example, the processes of Steps ST8001, ST8002, andST8004 of FIG. 44 or the processes of Steps ST8103, ST8002, and ST8004of FIG. 45 can be omitted.

If the central entity has the function of scheduling all the UEs beingserved by the cell included in the CoMP measurement set of the secondcell unified entity, the adjustment between CoMP measurement sets, theadjustment between CoMP active sets, or the adjustment between CoMPtransmissions is not necessary. This prevents a control delay andreduces a processing load.

If the central entity has the function of scheduling all the UEs beingserved by the cell included in the CoMP measurement set of the thirdcell unified entity, the adjustment between CoMP measurement sets, theadjustment between CoMP active sets, or the adjustment between CoMPtransmissions is not necessary. This prevents a control delay andreduces a processing load.

If the MAC functions which include the function difficult to be sharedin a plurality of radio areas exist, the second cell unified entity ishard to obtain. In such a case, if this function is shared, the thirdcell unified entity is useful, which shares, among the MAC functions toprevent a control delay and reduce a processing load when CoMP isperformed, at least the scheduling function in a plurality of radioareas.

Hereinafter, eNB refers to a device which has at least one cell and arelated interface in the seventh embodiment, the eighth embodiment, theninth embodiment, and the tenth embodiment. Also, sub eNB refers to adevice in which one or a plurality of sub cells and related interfacesare installed. The sub eNB also includes an RRH.

The central entity may be installed in the eNB, sub eNB, MME, and HeNBGWor installed in a new device. Herein, the new device in which thecentral entity is installed is referred to as a CoMP adjustment device.

The cell unified entity may be installed in the eNB, sub eNB, MME, andHeNBGW or may be installed in a new device. Herein, the new device inwhich the cell unified entity is installed is referred to as a cellcontroller. The CoMP adjustment device and the cell controller may bethe same device.

The interface between entities may differ depending on the device inwhich entities are mounted. For example, the S1 interface is usedbetween the MME and the eNB. The S1 interface is used between the HeNBGWand the HeNB. The S1 interface is used between the HeNBGW and the MME.The X2 interface is used between the eNBs. A dedicated line is usedbetween the eNB and the sub eNB. The dedicated line for the sub eNBsbeing RRHs may be also referred to as an optical fiber.

The seventh embodiment above can achieve similar effects to those of thefirst embodiment.

Eighth Embodiment

A problem to be solved in an eighth embodiment will be described below.3GPP has disclosed nothing about the UE mobility during CoMP. Thiscauses a problem that CoMP cannot be performed in the mobilecommunication system.

The solution to this problem will be described below. The serving cellbefore handover (hereinafter, also referred to as a “source cell”) stopsperforming CoMP. Specifically, the source cell stops performing CoMPwhen deciding to perform handover. The source cell stops performing CoMPbefore notifying the UE being a handover target of an instruction ofhandover. That is, the source cell does not use CoMP when notifying theUE being a handover target of an RRC connection reconfiguration messageincluding the mobility control information to which the parametersrequired for handover are mapped, and a handover command.

Specific examples of the method of stopping the execution of CoMP willbe disclosed below. A CoMP measurement configuration is released as themobile communication system.

The following three (1) to (3) will be disclosed as specific examples ofthe method of releasing a CoMP measurement configuration as the mobilecommunication system.

(1) If deciding to perform handover, the source cell requests the UEbeing a handover target to release the CoMP measurement configuration.The source cell may confirm that there is no continuing HARQ process andthen request the UE being a handover target to release the CoMPmeasurement configuration. When requesting the UE being a handovertarget to release the CoMP measurement configuration, the source cellmay notify together that handover is a cause.

The UE that has received the request to release the CoMP measurementconfiguration may release the CoMP measurement configuration and stopmeasuring the CSI-RS of the cell in the CoMP measurement set.

When releasing the CoMP measurement configuration, the UE may store thecell radio information (RAN information) included in the CoMPmeasurement set. The serving cell after handover (hereinafter, alsoreferred to as a “target cell”) may reset the CoMP measurement set atthe source cell. In such a case, a control delay can be prevented bystoring radio information by the UE.

The UE may store the radio information when releasing the CoMPmeasurement configuration due to handover. In this case, when requestingthe UE being a handover target to release the CoMP measurementconfiguration, the source cell may notify together that handover is acause.

The UE that has received a request to release the CoMP measurementconfiguration due to handover stores the radio information of the cellincluded in the CoMP measurement set. Meanwhile, the UE that hasreceived a request to release the CoMP measurement configuration due toa cause other than handover may avoid storing the radio information ofthe cell included in the CoMP measurement set.

The following 14 (a) to (n) will be disclosed as specific examples ofthe radio information of the CoMP measurement set.

(a) PCI, (b) downlink timing, (c) MIB information, (d) SIB information,(e) CSI-RS information, (f) TA, (g) transmission-reception timingdifference (TX-RX timing difference), (h) received MIMO information, (i)phase difference with other cell, (j) location information of UE duringmeasurement, (k) time information during measurement, (1) EDPCCHconfiguration, (m) reception quality information, and (n) combination of(a) to (m) above.

(2) If deciding to perform handover, the source cell requests the cellincluded in the CoMP measurement set to release the CoMP measurementconfiguration. The source cell may confirm that there is no continuingHARQ process, and then request the cell included in the CoMP measurementset to release the CoMP measurement configuration. The cell included inthe CoMP measurement set, which has received the request to release theCoMP measurement configuration, stops transmitting the CSI-RS.

(3) If deciding to perform handover, the source cell stops notifying thedata for CoMP directed to the UE1. Specifically, the source cell stopsnotifying the cell included in the CoMP measurement set of the datadirected to the UE1. The source cell may confirm that there is nocontinuing HARQ process and then stop notifying the data for CoMPdirected to the UE1. The source cell may stop notifying the cellincluded in the CoMP active set of the data directed to the UE1 ornotifying the CoMP transport point of the data directed to the UE1.

If deciding to perform handover, the source cell stops notifying CoMPscheduling for the UE1. Specifically, the source cell stops notifyingthe cell included in the CoMP measurement set of CoMP scheduling for theUE1. The source cell may confirm that there is no continuing HARQprocess and then stop notifying CoMP scheduling for the UE1. The sourcecell may stop notifying the cell included in the CoMP active set of CoMPscheduling for the UE1 or notifying the CoMP transport point of CoMPscheduling for the UE1.

The serving cell or the central entity may manage a CoMP measurementset. The CoMP measurement set may be managed per UE. The serving cell orcentral entity being the entity that manages the CoMP measurement setmay store the CoMP measurement configuration as the past informationalso after releasing the CoMP measurement configuration.

FIGS. 46 and 47 are diagrams showing an exemplary sequence of a mobilecommunication system in the eighth embodiment. FIGS. 46 and 47 arecontinuous with each other at a boundary BL9. FIGS. 46 and 47 show thesequence in the case where the UE1 moves from the sub cell1 to the subcell2 while CoMP is performed on the UE1 with the sub cell1 and the subcell2 being serving sub cells. This sequence shows the case where thecentral entity is configured in the serving cell, and thus, the centralentity and the serving cell are not particularly differentiated fromeach other and are referred to as a serving cell.

In Step ST8201, the cell1 judges whether or not to cause the UE1 toperform handover. If judging to cause the UE1 to perform handover, thecell1 stops performing CoMP on the UE1. Specifically, the cell1 decidesto release the CoMP measurement configuration. Also, if judging to causethe UE1 to perform handover, the cell1 decides a target cell being ahandover destination. In this exemplary operation, the cell2 is selectedas a target cell.

In Step ST8202, the cell1 requests the UE1 to release the CoMPmeasurement configuration (CoMP measurement set release). In StepST8203, the cell2 requests the UE1 to release the CoMP measurementconfiguration (CoMP measurement set release). This exemplary operationhas disclosed that CoMP is performed with the cell1 and the cell2 when arelease of the CoMP measurement configuration is requested.Alternatively, a request to release the CoMP measurement configurationmay be notified only from the cell1 without using CoMP in releasing theCoMP measurement configuration.

In Step ST8204, the UE1 that has received the request to release theCoMP measurement configuration releases the CoMP measurementconfiguration.

In Step ST8205, the cell1 being the serving cell requests the cell2being the cell included in the CoMP measurement set of the release ofthe CoMP measurement configuration.

In Step ST8206, the cell2 being the cell included in the CoMPmeasurement set notifies a response to the request to release the CoMPmeasurement configuration.

In Step ST8207, the cell2 being the cell included in the CoMPmeasurement set, which has received the request to release the CoMPmeasurement configuration in Step ST8205, stops transmitting the CSI-RS.

In Step ST8208, the cell1 being the serving cell stops notifying thecell2 being the cell included in the CoMP measurement set of the datadirected to the UE1. Specifically, the cell1 stops notifying the datafor CoMP directed to the UE1.

In Step ST8209, the cell1 stops transmitting the CSI-RS.

In Step ST8210, the cell1 being a source cell notifies the cell2 being atarget cell of a handover request.

In Step ST8211, the cell2 being a target cell judges whether or not itcan accept handover based on the resources and, if judging that it can,notifies the cell1 being a source cell of a handover request acceptance(handover request Ack).

In Step ST8212, the cell1 starts forwarding the data (data forwarding)related to the UE to the cell2. Specifically, the cell1 notifies thedata for HO directed to the UE1. The data for HO is notified in PDCP SDUdata (see Non-Patent Document 1).

In Step ST8213, the cell1 notifies the UE1 of an RRC connectionreconfiguration message including the mobility control information towhich the parameters required for handover are mapped. The cell1simultaneously instructs the UE1 to perform handover. The instruction toperform handover may also be referred to as a “handover command”.

In Step ST8214, the UE1 attempts the connection with the cell2 using theparameters received in Step ST8213. In other words, the UE1 transmitsRACH to the cell2 and transmits an RRC connection request.

In Step ST8215, the cell2 notifies the UE1 of timing advance (TA) as aresponse to the process of Step ST8214.

In Step ST8216, the UE1 notifies the cell2 of an RRC connectionreconfiguration complete.

The cell2 being a target cell that has received the RRC connectionreconfiguration complete may judge that the handover has been completed.Or, the cell2 may judge that the procedure of changing the serving cellhas been completed. The target cell that has received the RRC connectionreconfiguration complete may reconstruct multiple point communication(CoMP communication). This improves, after handover, the communicationquality by means of a plurality of radio links at a cell edge.

In Step ST8217, the cell2 that has received the notification of the RRCconnection reconfiguration complete from the UE1 in Step ST8216 performsthe path switch process.

In Step ST8218, the cell2 that has completed the path switch processnotifies the cell1 of a UE context release.

In Step ST8219, the cell1 that has received the notification of the UEcontext release from the cell2 in Step ST8218 releases the radioresources for the UE1.

The detailed operation in the case where CoMP is performed is similar tothat of the seventh embodiment. As disclosed in the seventh embodiment,the central entity may decide CoMP transmission points or the servingcell and the central entity may decide CoMP transmission pointstogether. The detailed operation in that case is similar to that of theseventh embodiment.

FIG. 48 is a diagram showing another exemplary sequence of the mobilecommunication system in the eighth embodiment. The sequence shown inFIG. 48 is similar to the sequence shown in FIGS. 46 and 47 , and thus,the same steps will be denoted by the same step numbers and commondescription will be omitted.

FIG. 48 shows the sequence of performing CoMP in the case where the cellunified entity is differentiated from the sub cells. This sequence showsthe case where the central entity is configured in the serving sub cellor in the central entity, and thus, the central entity and the servingsub cell are not particularly differentiated from the central entity andare referred to as a serving sub cell or central entity.

FIG. 48 shows the sequence in the case where the UE1 moves from the subcell1 to the sub cell2 while CoMP is performed on the UE1 with the subcell1 and the sub cell2 being serving sub cells.

The sequence shown in FIG. 48 can be used if the cell unified entity isthe first cell unified entity, the second cell unified entity, or thethird cell unified entity.

In Step ST8301, the cell unified entity judges whether or not to causethe UE1 to perform handover. If judging to cause the UE1 to performhandover, the cell unified entity stops performing CoMP on the UE1.Specifically, the cell unified entity decides to release the CoMPmeasurement configuration. Also, if judging to cause the UE1 to performhandover, the cell unified entity decides a target cell being a handoverdestination. In this exemplary operation, the cell2 is selected as atarget cell.

In Step ST8302, the cell unified entity requests the sub cell1 being thecell included in the CoMP measurement set to release the CoMPmeasurement configuration. The cell unified entity may request to stoptransmitting the CSI-RS, not limited to requesting to release the CoMPmeasurement configuration. Though not shown in FIG. 48 , the sub cell1may notify the cell unified entity of a response to the request torelease the CoMP measurement configuration.

In Step ST8303, the cell unified entity requests the sub cell2 being thecell included in the CoMP measurement set to release the CoMPmeasurement configuration. The cell unified entity may request to stoptransmitting the CSI-RS, not limited to requesting to release the CoMPmeasurement configuration. Though not shown in FIG. 48 , the sub cell2may notify the cell unified entity of a response to the request torelease the CoMP measurement configuration.

In Step ST8304, the sub cell1 being the cell included in the CoMPmeasurement set, which has received the request to release the CoMPmeasurement configuration, stops transmitting the CSI-RS.

In Step ST8305, the sub cell2 being the cell included in the CoMPmeasurement set, which has received the request to release the CoMPmeasurement configuration, stops transmitting the CSI-RS.

In Step ST8306, the cell unified entity stops notifying the sub cell2included in the CoMP measurement set of the data directed to the UE1.Specifically, the cell unified entity stops notifying the data for CoMPdirected to the UE1.

If the cell unified entity can recognize, for example, the loadcondition of the sub cell to judge whether or not the sub cell2 being atarget cell can accept handover, the processes equivalent to StepsST8210 and ST8211 of FIGS. 46 and 47 can be omitted. The provision ofthe cell unified entity as described above can prevent a control delay.

Considered here is the case where the cell unified entity has the PDCPfunctions shared in a plurality of radio areas. Specifically, the casewhere the cell unified entity has the PDCP functions in the radio areaof the serving sub cell and the radio area of the target sub cell incommon is considered. In this case, notification of the data for HObetween the serving sub cell and the target sub cell is not required.The process equivalent to Step ST8212 of FIG. 47 can be thus omitted. Acontrol delay can be prevented by providing the cell unified entity asdescribed above.

In Step ST8308, the cell unified entity notifies the UE1 of an RRCconnection reconfiguration message including the mobility controlinformation to which the parameters required for handover are mapped. Atthe same time, the cell unified entity instructs the UE1 to performhandover. The instruction to perform handover may also be referred to asa “handover command”.

In Step ST8309, the sub cell2 notifies the cell unified entity of theRRC connection reconfiguration complete received in Step ST8216.

Considered here is the case where the cell unified entity has the PDCPfunctions in a plurality of radio areas in common. Specifically, thecase where the cell unified entity has the PDCP functions in the radioarea of the serving sub cell and the radio area of the target sub cellin common is considered. In this case, the path switch process from theserving sub cell to the target sub cell is not required. The processequivalent to Step ST8217 of FIG. 47 can be thus omitted. A controldelay can be prevented by providing the cell unified entity as describedabove.

In Step ST8311, the cell unified entity that has completed the pathswitch process notifies the sub cell1 of a UE context release.

The detailed operation in the case where CoMP is performed is similar tothat of the seventh embodiment. The detailed operation of performingCoMP when the first cell unified entity is used and the detailedoperation of performing CoMP when the second cell unified entity is usedare similar to those of the seventh embodiment. Or, as disclosed in theseventh embodiment, the central entity may decide CoMP transmissionpoints, the serving sub cell and the central entity may decide CoMPtransmission points together, or the cell unified entity and the centralentity may decide CoMP transmission points together. The detailedoperation in that case is similar to that of the seventh embodiment.

The eighth embodiment described above can achieve the following effects.This embodiment has disclosed the handover method while CoMP isperformed. The disclosed method allows for handover while CoMP isperformed.

Control can be made easier in this embodiment than a tenth embodimentdescribed below. Also, compared with the tenth embodiment, for moving ofa UE being subjected to CoMP, this embodiment can allow a base stationand a user equipment to operate in a unified manner while preventing themobile communication system from becoming complicated, obtaining astable mobile communication system.

First Modification of Eighth Embodiment

This modification will disclose a specific example of the method ofstopping the execution of CoMP, which differs from that of the eighthembodiment.

As the mobile communication system, the CoMP active configuration isreleased. As the mobile communication system, the CoMP measurementconfiguration is not released, that is, is maintained.

The following six (1) to (6) will be disclosed as specific examples ofthe method of releasing a CoMP active configuration as the mobilecommunication system.

(1) If deciding to perform handover, the source cell requests the UEbeing a handover target to release the CoMP active configuration. Thesource cell may confirm that there is no continuing HARQ process andthen request the UE being a handover target to release the CoMP activeconfiguration.

The UE that has received the request to release the CoMP activeconfiguration releases the CoMP active configuration. The CoMPmeasurement configuration may not be released. The measurement of theCSI-RS of the in-CoMP-measurement-set cell may be continued.

The UE may store the radio information (RAN information) of the cellincluded in the CoMP active set when releasing the CoMP activeconfiguration. The target cell may reset the CoMP active configurationat the source cell. In such a case, the UE stores the radio information,preventing a control delay.

The UE may store the radio information when releasing the CoMP activeconfiguration due to handover. In this case, when requesting the UEbeing a handover target to release the CoMP active configuration, thesource cell may notify together that handover is a cause.

The UE that has received the request to release the CoMP activeconfiguration due to handover stores the radio information of the cellincluded in the CoMP active set. The UE that has received the request torelease the CoMP active configuration due to a cause other than handovermay avoid storing the radio information of the cell included in the CoMPactive set.

A specific example of the radio information of the CoMP active set issimilar to that of the radio information of the CoMP measurement set inthe eighth embodiment.

(2) If deciding to perform handover, the source cell does not requestthe cell included in the CoMP measurement set to release the CoMPmeasurement configuration. In other words, the cell included in the CoMPmeasurement set continues transmitting the CSI-RS.

(3) If deciding to perform handover, the source cell stops notifying thedata for CoMP directed to the UE1. Specifically, the source cell stopsnotifying the cell included in the CoMP measurement set of the datadirected to the UE1. The source cell may confirm that there is nocontinuing HARQ process and then stop notifying the data for CoMPdirected to the UE1. The source cell may stop notifying the cellincluded in the CoMP measurement set of the data directed to the UE1,notifying the cell included in the CoMP active set of the data directedto the UE1, or notifying the CoMP transport point of the data directedto the UE1.

(4) How to handle the CoMP measurement set will be described.

1) The CoMP measurement set at the source cell is continuously used alsoin the target cell. Specifically, the source cell notifies the targetcell of the CoMP measurement set at the source cell, with a handoverrequest. The target cell continuously uses the CoMP measurement set atthe source cell, which has been notified with the handover request, asthe CoMP measurement set of the UE being a handover target. In thiscase, if it can continuously use the CoMP measurement set at the sourcecell, the target cell notifies the source cell of this (Ack). The targetcell may notify that it can continuously use the CoMP measurement set atthe source cell, with a handover request acceptance (Handover requestAck).

If it cannot continuously use the CoMP measurement set at the sourcecell, the target cell notifies the source cell of this (Nack). Thetarget cell may notify that it cannot continuously use the CoMPmeasurement set at the source cell, with a handover request acceptance(Handover Request Ack).

If it continuously uses the CoMP measurement set at the source cell, thetarget cell may notify the CoMP measurement configuration again with anRRC connection reconfiguration message including the mobility controlinformation to which the parameters required for handover are mapped.This reduces a mismatch between the states of the target cell and theUE.

Or, the target cell may not notify the CoMP measurement configurationagain but may notify the information indicating that the CoMPmeasurement set at the source cell is continuously used also in thetarget cell, such as an indicator, with the RRC connectionreconfiguration message including the mobility control information towhich the parameters required for handover are mapped. This reduces anamount of control information.

Or, the target cell may statically or semi-statically decide to keep theCoMP measurement set during handover as the mobile communication system.This reduces an amount of control information. The information to beadded to the RRC connection reconfiguration message including themobility control information to which the parameters required forhandover are mapped is not required, allowing for construction of amobile communication system having backward compatibility.

The CoMP active set can be handled similarly to the CoMP measurementset.

(4-2) The source cell preliminarily notifies the UE of the CoMPmeasurement set scheduled to be used for the UE in the target cell. TheCoMP measurement set may be notified before handover.

If the target cell cannot continuously use the CoMP measurement set atthe source cell, the target cell notifies the CoMP measurement setscheduled to be used for the UE in the target cell. The CoMP measurementset scheduled to be used for the UE may be notified with a handoverrequest acceptance (Handover Request Ack).

The set preliminarily decided uniquely to the target cell may be used asthe CoMP measurement set scheduled to be used for the UE in the targetcell. For example, it may be the set to be decided depending on thelocation of the target cell, not to be decided per UE. This is becausethe UE does not perform measurement in the target cell.

The CoMP measurement set scheduled to be used for the UE in the targetcell may be notified with the RRC connection reconfiguration messageincluding the mobility control information to which the parametersrequired for handover are mapped. This allows the UE to preliminarilyknow the CoMP measurement set scheduled to be used for the UE in thetarget cell, preventing a control delay. After handover, the UE may usethe CoMP measurement set scheduled to be used for the UE in the targetcell.

The CoMP active set can be handled similarly to the CoMP measurementset.

(5) The UE that has received the handover command may continue measuringthe CSI-RS of the in-CoMP-measurement-set cell in the target cell.

(6) The cell1 that has been notified from the target cell that it hadcompleted the path switch process performs the following process. Thesource cell decides to release the CoMP measurement configuration forthe UE being a handover target. The source cell may stop transmittingthe CSI-RS. The source cell requests the cell included in the CoMPmeasurement set to release the CoMP measurement configuration. Thesource cell may confirm that there is no continuing HARQ process andthen request the cell included in the CoMP measurement set to releasethe CoMP measurement configuration.

The cell included in the CoMP measurement set, which has received therequest to release the CoMP measurement configuration, stopstransmitting the CSI-RS.

FIGS. 49 and 50 are diagrams showing an exemplary sequence of a mobilecommunication system in the first modification of the eighth embodiment.FIGS. 49 and 50 are continuous with each other at a boundary BL10. Thesequence shown in FIGS. 49 and 50 is similar to the sequence shown inFIGS. 46 and 47 , and thus, the same steps will be denoted by the samestep numbers, and common description will be omitted. FIGS. 49 and 50show the sequence in the case where the UE1 moves from the cell1 to thecell2 while CoMP is performed on the UE1 using the cell1 and the cell2being serving cells. This sequence shows the case where the centralentity is configured in the serving cell, and thus, the central entityand the serving cell are not particularly limited and are referred to asa serving cell.

In Step ST8400, the cell1 judges whether or not to cause the UE1 toperform handover. If judging to cause the UE1 to perform handover, thecell1 stops performing CoMP on the UE1. Specifically, the cell1 decidesto release the CoMP active configuration. If judging to cause the UE1 toperform handover, the cell1 decides a target cell being a handovertarget. In the exemplary operation, the cell1 selects the cell2 as thetarget cell.

In Step ST8401, the cell1 requests the UE1 to release the CoMP activeconfiguration (CoMP active set release). In Step ST8402, the cell2requests the UE1 to release the CoMP active configuration (CoMP activeset release). This exemplary operation has disclosed that CoMP isperformed with the cell1 and the cell2 when the release the CoMP activeconfiguration is requested. Alternatively, without CoMP used in therelease of the CoMP active configuration, only the cell1 may notify therequest to release the CoMP measurement configuration.

In Step ST8403, the UE1 that has received the request to release theCoMP active configuration releases the CoMP active configuration.

In Step ST8404, the cell1 that has received the notification of the UEcontext release from the cell2 in Step ST8218 decides to release theCoMP measurement configuration. The cell1 may decide to release the CoMPactive configuration in place of releasing the CoMP measurementconfiguration.

In Step ST8405, the cell1 being the serving cell requests the cell2being the cell included in the CoMP measurement set to release the CoMPmeasurement configuration.

In Step ST8406, the cell2 being the cell included in the CoMPmeasurement set notifies a response to the request to release the CoMPmeasurement configuration.

In Step ST8407, the cell2 being the cell included in the CoMPmeasurement set, which has received the request to release the CoMPmeasurement configuration in Step ST8405, stops transmitting the CSI-RS.

In Step ST8408, the cell1 that has decided to release the CoMPmeasurement configuration in Step ST8404 stops transmitting the CSI-RS.

The detailed operation in the case where CoMP is performed is similar tothat of the seventh embodiment. As disclosed in the seventh embodiment,the central entity may decide CoMP transmission points, or the servingcell and the central entity may decide CoMP transmission pointstogether. The detailed operation in that case is similar to that of theseventh embodiment.

FIGS. 51 and 52 are diagrams showing another exemplary sequence of themobile communication system in the first modification of the eighthembodiment. The sequence shown in FIGS. 51 and 52 is similar to thesequence shown in FIGS. 46 to 50 , and thus, the same steps will bedenoted by the same step numbers and common description will be omitted.FIGS. 51 and 52 are continuous with each other at a boundary BL11. FIGS.51 and 52 show the sequence of performing CoMP in the case where thecell unified entity is differentiated from the sub cell. This sequenceshows the case where the central entity is configured in the serving subcell or in the central entity, and thus, the central entity is notparticularly differentiated and is referred to as a serving sub cell ora central entity. FIGS. 51 and 52 show the sequence in the case wherethe UE1 moves from the sub cell1 to the sub cell2 while CoMP isperformed on the UE1 with the sub cell1 and the sub cell2 being servingsub cells. The sequence shown in FIGS. 51 and 52 can be used if the cellunified entity is the first cell unified entity, the second cell unifiedentity, or the third cell unified entity.

In Step ST8500, the cell unified entity judges whether or not to causethe UE1 to perform handover. If judging to cause the UE1 to performhandover, the cell unified entity stops performing CoMP on the UE1.Specifically, the cell unified entity decides to release the CoMP activeconfiguration. If judging to cause the UE1 to perform handover, the cellunified entity decides a target cell being a handover destination. Inthis exemplary operation, the sub cell2 is selected as the target cell.

If receiving the RRC connection complete in Step ST8309, in Step ST8501,the cell unified entity decides to release the CoMP measurementconfiguration. The cell unified entity may decide to release the CoMPactive configuration in place of releasing the CoMP measurementconfiguration.

In Step ST8502, the cell unified entity requests the sub cell1 being thecell included in the CoMP measurement set to release the CoMPmeasurement configuration. This may be a request to stop transmittingthe CSI-RS, not limited to the request to release the CoMP measurementconfiguration. Though not shown in FIGS. 51 and 52 , the sub cell1 maynotify the cell unified entity of the response to the request to releasethe CoMP measurement configuration.

In Step ST8503, the cell unified entity requests the sub cell2 being thecell included in the CoMP measurement set to release the CoMPmeasurement configuration. This may be a request to stop transmittingthe CSI-RS, not limited to the request to release the CoMP measurementconfiguration. Though not shown in FIGS. 51 and 52 , the sub cell2 maynotify the cell unified entity of a response to the request to releasethe CoMP measurement configuration.

In Step ST8504, the sub cell2 being the cell included in the CoMPmeasurement set, which has received the request to release the CoMPmeasurement configuration, stops transmitting the CSI-RS.

In Step ST8505, the sub cell1 being the cell included in the CoMPmeasurement set, which has received the request to release the CoMPmeasurement configuration, stops transmitting the CSI-RS.

The detailed operation in the case where CoMP is performed is similar tothat of the seventh embodiment. The detailed operation of performingCoMP using the first cell unified entity and the detailed operation ofperforming CoMP using the second cell unified entity are similar tothose of the seventh embodiment. Alternatively, as disclosed in theseventh embodiment, the central entity may decide CoMP transmissionpoints, or the cell unified entity and the central entity may decideCoMP transmission points together. The detailed operation in that caseis similar to that of the seventh embodiment.

The first modification of the eighth embodiment described above canachieve the following effects in addition to the effects of the eighthembodiment. The UE located at a position where CoMP is allowed or the UEthat has maintained a reception quality by being subjected to CoMP cancontinue CoMP measurement. Thus, CoMP can be started promptly even afterhandover, compared with the eighth embodiment. Also, the source cell canpreliminarily notify the UE of the CoMP measurement set scheduled to beused for the UE in the target cell. This eliminates the need fornotifying the CoMP measurement set again from the target cell, wherebyCoMP can be started promptly even after handover, compared with theeighth embodiment.

Second Modification of Eighth Embodiment

This modification will disclose another specific example of the methodof stopping the execution of CoMP, which differs from those of theeighth embodiment and the first modification of the eighth embodiment.

CoMP scheduling is not performed as the mobile communication system. Theselection of CoMP transmission points may be avoided.

Specific examples of the method of avoiding CoMP scheduling as themobile communication system will be disclosed below.

(1) If deciding to perform handover, the source cell notifies the UEbeing a handover target of nothing because the execution of CoMP isstopped. This allows for effective use of radio resources, compared withthe eighth embodiment and the first modification of the eighthembodiment. The CoMP measurement set or the CoMP active configurationneed not to be released. The CSI-RS of the in-CoMP-measurement-set cellmay be continued.

Other specific examples of the method of avoiding CoMP scheduling inthis modification are similar to the specific examples (2), (3), (4),(5), and (6) of the method of releasing the CoMP active configuration inthe first modification of the eighth embodiment, which will not bedescribed here.

FIGS. 53 and 54 are diagrams showing an exemplary sequence of a mobilecommunication system in the second modification of the eighthembodiment. FIGS. 53 and 54 are continuous with each other at a boundaryBL12. The sequence shown in FIGS. 53 and 54 is similar to the sequencesshown in FIGS. 46 and 47 , and FIGS. 49 and 50 , and thus, the samesteps will be denoted by the same step numbers and common descriptionwill be omitted. FIGS. 53 and 54 show the sequence in the case where theUE1 moves from the sub cell1 to the sub cell2 while CoMP is performed onthe UE1 with the sub cell1 and the sub cell2 being serving sub cells.This sequence shows the case where the central entity is configured atthe serving cell, and thus, the central entity and the serving cell arenot particularly differentiated from each other and are referred to as aserving cell.

In Step ST8601, the cell1 judges whether or not to cause the UE1 toperform handover. If judging to cause the UE1 to perform handover, thecell1 stops performing CoMP on the UE1. Specifically, the cell1 decidesnot to perform CoMP scheduling. Also, if judging to cause the UE1 toperform handover, the cell1 decides the target cell being a handovertarget. In this exemplary operation, the cell1 selects the cell2 as atarget cell.

In Step ST8602, the cell1 being the serving cell stops notifying thecell2 being the cell included in the CoMP transmission points of thedata directed to the UE1. Specifically, the cell1 stops notifying thedata for CoMP directed to the UE1.

The detailed operation in the case where CoMP is performed is similar tothat of the seventh embodiment. As disclosed in the seventh embodiment,the central entity may decide CoMP transmission points, or the servingcell and the central entity may decide CoMP transmission pointstogether. The detailed operation in that case is similar to that of theseventh embodiment.

FIG. 55 is a diagram showing another exemplary sequence of the mobilecommunication system in the second modification of the eighthembodiment. The sequence shown in FIG. 55 is similar to the sequencesshown in FIGS. 46 to 48 and FIGS. 51 and 52 , and thus, the same stepswill be denoted by the same step numbers and common description will beomitted.

FIG. 55 shows the sequence of performing CoMP in the case where the cellunified entity is differentiated from the sub cell. This sequence showsthe case where the central entity is configured in the serving sub cellor in the central entity, and thus, the central entity and the servingsub cell are not particularly differentiated and are referred to as aserving sub cell or central entity.

FIG. 55 shows the sequence in the case where the UE1 moves from the subcell1 to the sub cell2 while CoMP is performed on the UE1 with the subcell1 and the sub cell2 being serving sub cells. The sequence shown inFIG. 55 can be used if the cell unified entity is the first cell unifiedentity, the second cell unified entity, or the third cell unifiedentity.

In Step ST8701, the cell unified entity judges whether or not to causethe UE1 to perform handover. If judging to cause the UE1 to performhandover, the cell unified entity stops performing CoMP on the UE1.Specifically, the cell unified entity decides not to perform CoMPscheduling. Or, the serving sub cell may decide not to perform CoMPscheduling. Or, if judging to cause the UE1 to perform handover, thecell unified entity decides a target cell being a handover destination.In this exemplary operation, the sub cell2 is selected as a target cell.

In Step ST8702, the cell unified entity stops notifying the sub cell2being the cell included in the CoMP transmission points of the datadirected to the UE1. Specifically, the cell unified entity stopsnotifying the data for CoMP directed to the UE1.

The detailed operation in the case where CoMP is performed is similar tothat of the seventh embodiment. The detailed operation of CoMP in thecase where the first cell unified entity is used and the detailedoperation of CoMP in the case where the second cell unified entity isused are similar to those of the seventh embodiment. As disclosed in theseventh embodiment, the central entity may decide CoMP transmissionpoints, or the cell unified entity and the central entity may decideCoMP transmission points together. The detailed operation in that caseis similar to that of the seventh embodiment.

The second modification of the eighth embodiment described above canachieve similar effects to those of the eighth embodiment and the firstmodification of the eighth embodiment.

Ninth Embodiment

A problem to be solved in a ninth embodiment will be described below. Inthe method of the eighth embodiment, the execution of CoMP is stoppedtemporarily. As a result, the reception quality of the link, which hasbeen maintained through execution of CoMP, suddenly deteriorates,causing a problem that communication is disconnected. As a specificexample, it is conceivable that the UE cannot normally receive the RRCconnection reconfiguration message including the mobility controlinformation to which the parameters required for handover are mapped,which is transmitted from the source cell. Thus, the UE cannot normallyperform handover, and its communication is disconnected.

A solution to the above-mentioned problem that communication isdisconnected will be described below. During the handover process, thesource cell continues performing CoMP. In other words, during thehandover process, the network including a cell and a sub cell does notrelease the configuration regarding CoMP. Specifically, the CoMPmeasurement set and the CoMP active configuration are not released. Whennotifying the UE being a handover target of the RRC connectionreconfiguration message including the mobility control information towhich the parameters required for handover are mapped and of a handovercommand, the source cell performs CoMP.

Specific examples during the handover process include a handoverpreparation phase, a handover execution phase, and a handover completionphase (see Chapter 10.1.2.1 of Non-Patent Document 1).

The following three (1) to (3) will be disclosed as specific examples ofthe method in which the source cell continues performing CoMP.

(1) When notifying the UE being a handover target of the RRC connectionreconfiguration message including the mobility control information towhich the parameters required for handover are mapped and of a handovercommand, the source cell performs CoMP.

(2) The source cell requests the UE being a handover target to releasethe CoMP measurement configuration with the RRC connectionreconfiguration message including the mobility control information towhich the parameters required for handover are mapped, or afternotifying the RRC connection reconfiguration message. The source cellmay request to release the CoMP active configuration in place ofrequesting to release the CoMP measurement configuration.

The UE that has received the request to release the CoMP measurementconfiguration may release the CoMP measurement configuration and stopmeasuring the CSI-RS of the in-CoMP-measurement-set cell. The UE mayrelease the CoMP measurement configuration at the source cell and maystop measuring the CSI-RS of the cell in CoMP measurement set at thesource cell.

Or, as a mobile communication system, the RRC connection reconfigurationmessage including the mobility control information to which theparameters required for handover during the execution of CoMP are mappedmay also imply a request to release the CoMP measurement configurationor a request to release the CoMP active configuration. This reduces anamount of control information. In this case, during CoMP, the UE, whichhas received the RRC connection reconfiguration message including themobility control information to which the parameters required forhandover are mapped, may release the CoMP measurement configuration, mayrelease the CoMP active configuration, or may stop measuring the CSI-RSof the in-CoMP-measurement-set cell.

The UE may store the radio information when releasing the CoMPmeasurement configuration due to handover. A specific example thereof issimilar to that of the eighth embodiment, which will not be describedhere.

(3) The cell1 that has been notified that the path switch process hadbeen completed from the target cell performs the following process.Specific examples of the notification that the path switch process hasbeen completed include a notification of UE context release. The sourcecell stops notifying the data for CoMP directed to the UE1.Specifically, the source cell stops notifying the cell included in theCoMP measurement set of the data directed to the UE1. The source cellmay confirm that there is no continuing HARQ process and then stopnotifying the data for CoMP directed to the UE1. The source cell maystop notifying the cell included in the CoMP measurement set of the datadirected to the UE1, notifying the cell included in the CoMP active setof the data directed to the UE1, or notifying the CoMP transport pointof the data directed to the UE1.

Specific examples of another method of continuing performing CoMP by thesource cell in this modification are similar to the specific examples(4), (5), and (6) of the method of releasing the CoMP activeconfiguration in the first modification of the eighth embodiment, whichwill not be described here.

FIGS. 56 and 57 are diagrams showing an exemplary sequence of a mobilecommunication system in a ninth embodiment. FIGS. 56 and 57 arecontinuous with each other at a boundary BL13. The sequence shown inFIGS. 56 and 57 is similar to the sequences shown in FIGS. 46 and 47 andFIGS. 49 and 50 , and thus, the same steps will be denoted by the samestep numbers and common description will be omitted. FIGS. 56 and 57show the sequence in the case where the UE1 moves from the cell1 to thecell2 while CoMP is performed on the UE1 with the cell1 and the cell2being serving cells. This sequence shows the case where the centralentity is configured in the serving cell, and thus, the central entityand the serving cell are not particularly differentiated from each otherand are referred to as a serving cell.

In Step ST8801, the cell1 judges whether or not to cause the UE1 toperform handover. If judging to cause the UE1 to perform handover, thecell1 decides to continue performing CoMP on the UE1 by the source cellduring the handover process. Also, if judging to cause the UE1 toperform handover, the cell1 decides a target cell being a handoverdestination. In this exemplary operation, the cell1 selects the cell2 asa target cell.

In Step ST8802, the cell1 notifies the UE1 of the RRC connectionreconfiguration message including the mobility control information towhich the parameters required for handover are mapped. In Step ST8803,the cell2 notifies the UE1 of the RRC connection reconfiguration messageincluding the mobility control information to which the parametersrequired for handover are mapped. At the same time, the cell1 instructsthe UE1 to perform handover. In this exemplary operation, CoMP isperformed with the cell1 and the cell2 in notifying the RRC connectionreconfiguration message.

In Step ST8804, the UE1 that has received the request to release theCoMP measurement configuration releases the CoMP measurementconfiguration.

In Step ST8805, the cell1 that has received the UE context release inStep ST8218 stops notifying the cell included in the CoMP measurementset of the data directed to the UE1. Specifically, the cell1 stopsnotifying the data for CoMP directed to the UE1.

The detailed operation in the case where CoMP is performed is similar tothat of the seventh embodiment. As disclosed in the seventh embodiment,the central entity may decide CoMP transmission points, or the servingcell and the central entity may decide CoMP transmission pointstogether. The detailed operation in that case is similar to that of theseventh embodiment.

FIGS. 58 and 59 are diagrams showing another exemplary sequence of themobile communication system in the ninth embodiment. FIGS. 58 and 59 arecontinuous with each other at a boundary BL14. The sequence shown inFIGS. 58 and 59 is similar to the sequences shown in FIGS. 46, 47 and 48, FIGS. 51 and 52 , and FIGS. 56 and 57 , and thus, the same steps willbe denoted by the same step numbers and common description will beomitted.

FIGS. 58 and 59 show the sequence of performing CoMP in the case wherethe cell unified entity is differentiated from the sub cell. Thissequence shows the configuration in which the central entity isconfigured in the serving sub cell or in the central entity, and thus,the central entity and the serving sub cell are not particularlydifferentiated from the central entity, which are referred to as aserving sub cell or a central entity.

FIGS. 58 and 59 show the sequence in the case where the UE1 moves fromthe sub cell1 to the sub cell2 while CoMP is performed on the UE1 withthe sub cell1 and the sub cell2 being serving sub cells. The sequenceshown in FIGS. 58 and 59 can be used if the cell unified entity is thefirst cell unified entity, the second cell unified entity, or the thirdcell unified entity.

In Step ST8901, the cell unified entity judges whether or not to causethe UE1 to perform handover. If judging to cause the UE1 to performhandover, the cell unified entity decides to continue CoMP on the UE1 bythe source cell during the handover process. Also, if judging to causethe UE1 to perform handover, the cell unified entity decides a targetcell being a handover destination. In this exemplary operation, the cellunified entity selects the sub cell2 as a target cell.

In Step ST8902, the cell unified entity that has received RRC connectioncomplete in Step ST8309 stops notifying the cell included in the CoMPmeasurement set of the data directed to the UE1. Specifically, the cellunified entity stops notifying the data for CoMP directed to the UE1.

The detailed operation in the case where CoMP is performed is similar tothat of the seventh embodiment. Or, as disclosed in the seventhembodiment, the central entity may decide CoMP transmission points, orthe serving cell and the central entity may decide CoMP transmissionpoints together. The detailed operation in that case is similar to thatof the seventh embodiment.

The ninth embodiment described above can achieve the following effectsin addition to the effects of the eighth embodiment and the firstmodification of the eighth embodiment. The handover process prevents thereception quality from suddenly deteriorating at the source cell. As aspecific example, the RRC connection reconfiguration message includingthe mobility control information to which the parameters required forhandover are mapped, transmitted from the source cell, is transmittedusing CoMP. This allows the UE to normally receive the RRC connectionreconfiguration message.

First Modification of Ninth Embodiment

A problem to be solved in a first modification of the ninth embodimentwill be described below. 3GPP discloses the operation when a radio linkfailure occurs as follows (see Chapter 10.1.6 of Non-Patent Document 1).The radio link failure also refers to a handover failure. 3GPP disclosesthe conditions for successful reconnection of the UE when a radio linkfailure occurs. One example of the conditions for successfulreconnection is the case where the UE selects an eNB that stores the UEcontext as a reconnection destination.

When a handover failure occurs, the target cell does not notify thesource cell of UE context release. The source cell thus does not releasethe context of the UE being a handover target. Also, when a handoverfailure occurs, the UE selects the source cell as a reconnectiondestination, meeting the conditions for successful reconnection.

It is conceivable that while the UE being subjected to CoMP moves, thereception quality will be maintained through the execution of CoMP bythe source cell. When handover fails, accordingly, the reception qualityof the link is poor even if the source cell is selected as areconnection destination, causing a problem that reconnection will belikely to fail.

A solution to the problem that the reconnection will be likely to failwill be described below. If selecting the source cell as a reconnectiondestination, the UE, which has detected a handover failure while movingduring CoMP, resets a CoMP measurement set at the source cell. The UEmay restart measuring the CSI-RS of the in-CoMP-measurement-set cell atthe source cell. Or, a CoMP active set at the source cell is reset.

In the first modification of the ninth embodiment, the source cell isnotified that the path switch process has been completed from the targetcell, and then, releases the CoMP measurement configuration for the UEbeing a handover target. If a handover failure occurs, the source cellis not notified that the path switch process has been completed from thetarget cell. During a handover failure, the source cell does not releasethe CoMP measurement configuration for the UE being a handover target.This does not cause a mismatch between the CoMP measurement sets of theUE and the network that includes a cell and a sub cell.

In this case, the UE may store radio information when releasing a CoMPmeasurement configuration due to handover. A specific example thereof issimilar to that of the eighth embodiment, which will not be describedhere.

The first modification of the ninth embodiment can achieve the followingeffects. If handover fails, the source cell is selected as areconnection destination, keeping the reception quality of the linkthrough the execution of CoMP. Therefore, reconnection is highly likelyto succeed.

Tenth Embodiment

A problem to be solved in the tenth embodiment will be described below.The eighth embodiment and the modifications thereof, and the ninthembodiment and the modification thereof are configured such that in theset CoMP active set or CoMP measurement set, if the UE performingmultiple point communication (CoMP communication) performs handover,that is, if the UE changes the serving cell, CoMP communication isstopped to be switched to single point communication with the servingcell and, after the completion of the procedure of changing the servingcell, multiple point communication is constructed again.

FIGS. 60 and 61 are diagrams for describing the concept of CoMPcommunication among a plurality of sub eNB devices and a UE. FIG. 60shows the case where three sub eNB (Sub-eNB) devices, namely, a firstsub eNB device (Sub-eNB1) 10104, a second sub eNB device (Sub-eNB2)10105, and a third sub eNB device (Sub-eNB3) 10106, and a first UE (UE1)10107 perform CoMP communication. The three sub eNB devices 10104 to10106 define three cell areas 10101 to 10103.

FIG. 61 shows the case where the first UE (UE1) has moved from thelocation indicated by reference numeral “10207” to the locationindicated by reference numeral “10208”. In FIG. 61 , the first UE (UE1)10207, 10208 corresponds to the first UE (UE1) 10107 of FIG. 60 , firstto third sub eNB devices (Sub-eNB1 to Sub-eNB3) 10204 to 10206correspond to the first to the third sub eNB devices (Sub-eNB1 toSub-eNB3) 10104 to 10106 of FIG. 60 , and cell areas 10201 to 10203 ofthe sub eNB devices 10204 to 10206 correspond to the cell areas 10101 to10103 of FIG. 60 .

When the first UE (UE1) moves from the location indicated by referencenumeral “10207” to the location indicated by reference numeral “10208”,the process of changing the serving cell is required, which stops CoMPcommunication. In this case, the first UE (UE1) 10208 communicates with,for example, the first sub eNB device (Sub-eNB1) 10204.

The serving cell is often changed when the UE is located at the edge ofthe cell of which coverage the UE is in, as shown in FIG. 61 . It isconceivable in this positional relationship that the communicationquality of the communication link between the serving cell and the UEwill degrade by an amount for the distance therebetween. It is alsoconceivable that the serving cell will be changed per se to be changedto a cell having a better communication quality of the communicationlink.

If CoMP communication is stopped when the serving cell is changed, asshown in FIG. 61 , gains of the communication quality in the multipointcommunication (CoMP communication) over single point communicationcannot be obtained while the above-mentioned communication is stopped,which allows for only communication with low communication quality. Thismay lead to a situation in which the procedure of changing a servingcell per se cannot be completed.

An object of CoMP communication is to improve the communication qualitywith a plurality of radio links at a cell edge. This also shows that theabove-mentioned problem is serious.

The following problem is cited as another problem. Although the processof changing the serving cell by the UE, which is disclosed in, forexample, Non-Patent Document 1, involves the recovery process throughretransmission, it permits a partial loss of packets at Layer 2 duringthe procedure of the process.

Unfortunately, a loss of packets unnecessarily increases an unnecessarycommunication traffic associated with a change of the serving cell.Considering an influence of the quality deterioration caused by stoppingCoMP communication, the influence of a loss of packets may increasefurther.

A solution to the problem in the tenth embodiment will be describedbelow. To solve the above-mentioned problem, in this embodiment, theserving cell is changed while CoMP communication is continued. FIG. 62is a diagram for describing a change of the serving cell in the tenthembodiment. FIG. 62 shows the case where the first UE (UE1) moves fromthe location indicated by reference numeral “10307” to the locationindicated by reference numeral “10308” while CoMP communication isperformed.

The cells to be included in the CoMP active set or CoMP measurement setfor CoMP are likely to be geographically adjacent cells, and a servingcell to become a change destination is likely to be selected from thosecells. FIG. 62 shows the case where among cells including first to thirdsub eNB devices (Sub-eNB 1 to Sub-eNB3) 10304 to 10306, the serving cellof the CoMP active set is changed from the cell including the first subeNB device (Sub-eNB1) 10304 to the cell including the second sub eNBdevice (Sub-eNB2) 10305.

In this case, the communication link quality of the cell being a changesource (hereinafter, referred to as a “source cell”) of the serving cellis likely to become insufficient due to moving of the UE, and thecommunication link quality of the cell being a change destination(hereinafter, referred to as a “target cell”) of the serving cell islikely to become sufficient thanks to a reduced distance. Therefore,changing the serving cell while performing CoMP communication agreeswith the object of CoMP communication and allows the serving cell to bechanged in a good environment, which is highly effective.

The serving cell is changed while CoMP communication is performed, andthus, a conventional instantaneous interruption of physical layers canbe expected to be minimized. Therefore, Layer 2 of the source cell isassociated with Layer 2 of the target cell to minimize a packet loss atthe existing Layer 2, suppressing an unnecessary traffic increase due toa change of the serving cell.

For this, the following four processes (1) to (4) are added to theprocedure of changing a serving cell.

(1) The source cell notifies the target cell of a CoMP set.

The data unit before, during, or after the process at Layer 2 (PDCP/RLC)excluding PDCP SDU (RLC SDU, RLC PDU, and other data unit duringprocess) are not discarded, and are forwarded from the source cell tothe target cell with the related parameters.

(3) Switching to the target cell is performed considering that thesource cell will complete at least the process related to the physicallayer process such as the HARQ process of the processes at Layer 2.

(4) The procedure of preserving the transmission order at the sourcecell and the target cell is added in data transmission at Layer 2(PDCP/RLC) (re-establishment of the RLC, described in TS36.322 V10.0.0(hereinafter, referred to as “Reference 8”) by 3GPP, is not performed).

Although this embodiment does not describe forwarding of the MAC dataunit, the data unit before starting the HARQ process at MAC layer can beforwarded to the target cell similarly to RLC/PDCP.

FIGS. 63 to 66 are diagrams showing an exemplary sequence of a mobilecommunication system in a tenth embodiment. FIGS. 63 and 64 arecontinuous with each other at a boundary BL15. FIGS. 64 and 65 arecontinuous with each other at a boundary BL16. FIGS. 65 and 66 arecontinuous with each other at a boundary BL17.

This sequence shows an example of the case where in communicationbetween the UE and the E-UTRAN, the UE performs CoMP communication withthree cells as the CoMP active set or CoMP measurement set, and changesthe serving cell among those cells. Though not shown in FIGS. 63 to 66 ,for example, scheduling from the cell to the UE is notified over thePDCCH or the like.

Herein, among the cells in the CoMP active set or the CoMP measurementset, the serving cell before the serving cell is changed is taken as asource cell, the serving cell after the serving cell is changed is takenas a target cell, and the other one cell that does not serve as theserving cell in this sequence is taken as a non-serving cell.

Each cell configures the PHY, MAC, RLC, PDCP, and RRC layers and, as arule, each of those layers has at least the function described in thespecifications of 3GPP.

At the beginning of the sequence, first, the UE performs CoMPcommunication where three cells configure the CoMP active set or theCoMP measurement set. In this case, in Steps ST10401 to ST10404, thelink for transmitting a MAC data unit and the link for notifying thescheduling information on the data unit scheduled at the MAC of thesource cell exist between the source cell and the target cell andbetween the source cell and the non-serving cell. These links may becollectively referred to as a “MAC-data-unit-related transmission link”.

The link is described here as a logical one, an installation manner ofwhich differing depending on actual installation. For example, if thesource cell and the target cell are installed as different eNBs, thecommunication interface therebetween may be an X2 interface. Not limitedto the MAC-data-unit-related transmission link, a logical link isassumed to exist for a communication path for communication betweencells.

In Step ST10405, the source cell performs the HO decision process.Specifically, the source cell decides to perform HO to the target cell.

After that, in Step ST10406, the RRC of the source cell issues a HOrequest. Specifically, for example, the RRC of the source cell notifiesthe RRC of the target cell of whether or not CoMP needs to be continued(proposal), which is currently operated in communication with a UE tobecome a target, and of the measurement information on the communicationbetween the CoMP active set and the CoMP measurement set, and the cellsthereof. Here, whether or not CoMP needs to be continued (proposal) maybe judged from the CoMP set and needs not to be explicitly notified.

In Step ST10408 of Step ST10407, the RRC of the target cell that hasreceived the HO request in Step ST10406 decides a CoMP set candidate atthe target cell based on, for example, the information contained in theHO request, the traffic situation of its own cell, and the CoMPcooperating set information.

After that, in Steps ST10408 and ST10455, the RRC of the target cellnotifies the CoMP active set being a CoMP set candidate or the cellsincluded in the CoMP measurement set, in this example, the source celland the non-serving cell, of a CoMP communication request (CoMP request)to the UE to become a target.

The source cell and the non-serving cell that have received the requestin Steps ST10408 and ST10455 confirm the traffic of itself and thesituation regarding other communication resource and, in Steps ST10409and ST10456, notify the target cell of the results as a CoMP response.

In Step ST10410, the target cell that has received the CoMP responses inSteps ST10409 and ST10456 decides a CoMP set based on the results.

After that, in Step ST10411, based on the CoMP set judgment results, thetarget cell notifies the source cell of the response mainly includingthe information on whether or not HO is allowed, whether or not CoMP canbe continued, and a supportable CoMP set, as the HO response. Here,whether or not CoMP can be continued needs not to be explicitlynotified, assuming that it is judged from the CoMP set. The target cellneeds not to notify a supportable CoMP set if continuing the CoMP set atthe source cell that has been received in Step ST10406.

In Step ST10412, the source cell that has received a response indicatingthat HO is allowed (OK) transmits, to the UE, a message indicating thatthe serving cell will be changed, which contains the informationindicating that CoMP is continued and indicating a CoMP set, as an RRCconnection reconfiguration. The transmission of this message allows theUE that has received this message to operate differently from the casewhere the UE has received “RRC Connection Reconfiguration” described inNon-Patent Document 1, Reference 1, and the like.

The following three (1) to (3) will be disclosed as specific examples ofthe operation different from the case where the UE has received “RRCConnection Reconfiguration”.

“Re-establishment” of the RLC is not performed.

The MAC is not reset.

“Re-establishment” of the PDCP is not performed.

The following six (1) to (6) will be disclosed as specific examples ofthe message indicating that a serving cell continuing CoMP is changed.

Whether or not CoMP can be continued is indicated.

Whether or not to re-establish the RLC is indicated.

Whether or not to reset the MAC is indicated.

Whether or not to re-establish the PDCP is indicated.

Combination of (1) to (4) above.

“RRC Connection Reconfiguration” while CoMP is performed or while a CoMPset is set is statically decided to indicate (1) to (5) above. Thiseliminates the need for newly providing a message, compared with (1) to(5) described above, preventing the mobile communication system frombecoming complicated.

The following three (1) to (3) will be disclosed as specific examples ofthe method of notifying a message indicating that the serving cellcontinuing CoMP is changed.

An RRC connection reconfiguration indicator or an information element isnewly added.

An indicator or an information element is newly added to mobilitycontrol information.

Other message is newly provided.

In Step ST10412 as well as in Steps ST10413 and ST10414, as a request tostop and forward the PDCP process (PDCP stop and forward request) and arequest to stop and forward the RLC process (RLC stop and forwardrequest), the RRC of the source cell instructs the PDCP and RLC tobecome targets to stop the process on the unprocessed data unit and stopdownlink transmission to the MAC and RLC and also instructs to transmit,to the target cell, the “data unit and the related parameters that havenot been transmitted for the higher layers in uplink and for lowerlayers in downlink”. The request to stop and forward the RLC process(RLC stop and forward request) is newly provided in Step ST10414,allowing the data unit at Layer 2 (RLC) and the related parameters to beforwarded from the source cell to the target cell. Data forwarding ofthe RLC data is also allowed.

In Steps ST10417 to ST10422, the PDCP and RLC of the source cell thathave received the instruction stop and forward the process and, in StepsST10423 and ST10425, continue forwarding the data unit to be received ateach layer after the instruction to the target cell. A timer may bemanaged for judgment per layer in the method of stopping forwarding, orforwarding may be stopped to coincide with the completion of the MACtimer as described below. If the HO completion by the UE in Step ST10457described below is notified, an instruction thereof may be used injudging to stop forwarding.

In this forwarding, the level of the data unit, and the packets to beforwarded with the PDU, SDU, and the like are transmitted to the targetcell in such a manner that the process order thereof becomes apparent ifthe HO did not exist. For example, the process order and thetransmission order are caused to agree with each other, or theinformation on the process order is added.

Also for the RLC retransmission packets described in Reference 8, theinformation indicating this is added to the PDU, and the information istransmitted to the target cell in the processing order, for example, thenumerical order of the RLC or SN.

In the transmission process at each layer, a data unit that has notcompleted the transmission process may be transmitted together at alayer lower than each layer (RLC for PDCP, MAC for RLC). In this case,if the target cell confirms the completion of the data unit transmissionprocess at a corresponding lower layer, the data unit is not transmittedbut is discarded.

Further, in Step ST10415, the RRC of the source cell notifies the MACthat HO has been started. Specifically, the RRC of the source cellnotifies the start of HO (HO ind).

The MAC of the source cell that has been notified the start of HOcontinues the process until forwarding of the currently held data unitis completed as to downlink. To judge that the process is to be stopped,a timer may be provided to set a maximum process completion time. Inthis case, the process is stopped upon completion of the process orexpiration of the timer.

In this case, the HARQ process (see TS36.321 V10.4.0 (hereinafter,referred to as “Reference 9”) by 3GPP needs to be taken into account.The HARQ process is of an N process stop-and-wait system and thus needsto set a timer value in consideration of the retransmission.

For uplink, the process of receiving a data unit from a UE is continued.To judge that the process is to be stopped, a timer different from theabove-mentioned timer is provided to stop the process after the MACprocess of the UE is completed. As in downlink, the HARQ process needsto be taken into account in the time before the timer expires. For easyinstallation, the same timer may be used in uplink and downlink. If theHO completion by the UE described below is notified, an instructionthereof may be used in judging to stop forwarding.

Similarly to the cell, the UE that has received the RRC connectionreconfiguration message in Step ST10412 stops the RLC and PDCP processesin UL, in the process of stopping UL RLC/PDCP in Step ST10416.

For uplink, the MAC continues the process until forwarding of thecurrently held data unit is completed, as in the cell. A timer isprovided to judge that the process is to be stopped and, in StepST10424, the UE judges whether or not the MAC process has been completedor the processing timer has expired.

For downlink, the process of receiving a data unit from the cell iscontinued. To judge that the process is to be stopped, a timer differentfrom the above-mentioned timer is provided to stop the process after thecompletion of the MAC process by the cell. As in uplink, the HARQprocess needs to be taken into account in the time before the timerexpires. As in this embodiment, for easier installation, the same timermay be used in uplink and downlink.

If the MAC process has been completed or the processing timer hasexpired in Step ST10424, in Step ST10428, the UE transmits, to thetarget cell, an RRC connection reconfiguration complete messagecorresponding to the RRC connection reconfiguration. A synchronisationprocess of Step ST10426 and a TA notification process of Step ST10427are performed as required.

After that, the UE performs communication in accordance with schedulingof the MAC of the target cell, where the target cell is a serving cell.Whether or not the message of the procedure of changing a serving cellin, for example, Step ST10427 shows CoMP communication depends on thepresence/absence of the process of Step ST10429 and the completionstatus of the process of Step ST10442, described below. If the processof Step ST10429 has not been performed and the process of Step ST10442has been completed, CoMP communication is allowed.

In Step ST10457 of Step ST10429, the RRC of the target cell that hasreceived the RRC connection reconfiguration complete message in StepST10428 notifies the source cell that the UE has completed a change ofthe serving cell (UE HO Complete Ind). In Step ST10430, the RRC of thetarget cell also notifies the non-serving cell that the UE has completeda change of the serving cell (UE HO Complete Ind).

In Step STST10433, the source cell, which has recognized that theserving cell had been changed from the notification that the UE hadcompleted a change of the serving cell in Step ST10457, completes theMAC, RLC, and PDCP processes of the UE to become a target. After theprocess has been completed, in Step ST10458, the source cell notifiesthe target cell that the source cell has completed the process (Sourcecell process complete).

In Steps ST10431, ST10432, and ST10435, the non-serving cell, which hasrecognized that a change of the serving cell had been completed from thenotification that the UE had completed the change of the serving cell inStep ST10430, completes the MAC process of the UE to become a target.After the process has been completed, in Step ST10434, the non-servingcell notifies the target cell that the source cell had completed theprocess (Source cell process complete).

A series of processes of Step ST10429 is the procedure for strictlypreventing a mismatch occurring in the completion of the process betweenthe UE and each cell, and is applicable as the procedure of completingthe process at the source cell when the serving cell performing CoMP ischanged. The processes of Step ST10429 may be omitted for simplifyingthe processing procedure and increasing the speed at which the servingcell is changed.

In Step ST10442, the target cell, which has transmitted a HO response inStep ST10411, performs the processes of Steps ST10436 and ST10437. Afterthat, in Steps ST10438 and ST10440, the target cell sets data unit linksbetween the MAC thereof and the MAC of the non-serving cell and betweenthe MAC thereof and the MAC of the non-serving cell and, in StepsST10439 and ST10441, sets scheduling information links.

A series of processes of Step ST10442 may be performed at an appropriatetiming during an interval between the transmission of a HO response inStep ST10411 and a data request in Step ST10449. If the data unit linkand the scheduling information link between the MACs of the source cellside and the links of the target cell side in Steps ST10401 to ST10404cannot be established together, as shown in FIGS. 63 to 66 , the linksmay be established after HO has been completed.

In Steps ST10443, ST10444, and ST10445, the RRC of the target cell,which has received an RRC connection reconfiguration completenotification in Step ST10428, notifies the MAC, RLC, and PDCP thereofthat the serving cell has been changed, that is, that the UE hascompleted HO (UE HO Complete Ind). After that, the processes of StepsST10446 to ST10454 are performed.

The MAC of the target cell that has received the notification of UE HOComplete Ind in Step ST10443 checks whether or not a MAC transmissionlink to become a target is established. If the link is established, theMAC of the target cell performs the process in accordance with a requestfrom the UE for uplink or, for downlink, requests data from the RLC andperforms the MAC process on the data transmitted from the RLC. Thecommunication with the cell for which the MAC transmission link isestablished is started together. If the MAC transmission link to becomea target is not established, the MAC of the target cell establishes theMAC transmission link to become a target and then performs theabove-mentioned process.

For uplink, the RLC of the target cell that has received thenotification of UE HO Complete Ind in Step ST10444 first performs theprocess on the forwarded data units in the transmission order, using theparameters transmitted in association with the data units, and then,successively processes the uplink RLC PDU transmitted from the MAC.

For downlink, when being requested to transmit data from the datatransmission request (DATA request) in Step ST10449, the RLC of thetarget cell processes the forwarded data units for retransmission andtransmits the RLC PDU to the MAC, and then, processes the forwarded dataunit for initial transmission and transmits the RLC PDU to the MAC.

In Step ST10453, the RLC that has processed the forwarded data unitsrequests the PDCP to transmit data, and then, processes the datareceived from the PDCP.

In Step ST10446, the PDCP of the target cell that has received thenotification of UE HO Complete Ind in Step ST10445 performs the S1interface path switch process to set a switch to the target cell. Foruplink, the PDCP of the target cell processes the forwarded data unitsin the transmission order, using the parameters transmitted inassociation with the data units, and then, successively processes theuplink PDCP PDU transmitted from the RLC.

For downlink, when being requested to transmit data from DATA request ofStep ST10453, the PDCP of the target cell processes the forwarded dataunits and transmits the PDCP PDU to the RLC.

As described above, in this embodiment, the data unit at each layer istransmitted between cells in the clarified process order assumed by thesource cell. Then, the target cell performs the processes in the processorder, and then performs the data unit processes from the higher layerto the lower layer. For downlink, data transmission is started inaccordance with the request from the lower layer of the target cell.This allows for the processes in which the transmission order ispreserved between the source cell and the target cell. Therefore,communication can be continued without performing RLC re-establishmentdescribed in Reference 8.

First Modification of Tenth Embodiment

A first modification of the tenth embodiment shows an example in which,when the configuration of the tenth embodiment includes a CoMP centralentity that performs CoMP MAC level coordinated control, a serving cellis changed while performing CoMP communication.

FIGS. 67 to 70 are diagrams showing an exemplary sequence of a mobilecommunication system in the first modification of the tenth embodiment.FIGS. 67 and 68 are continuous with each other at a boundary BL18. FIGS.68 and 69 are continuous with each other at a boundary BL19. FIGS. 69and 70 are continuous with each other at a boundary BL20.

This sequence shows, similarly to the sequence shown in FIGS. 63 to 66 ,an example in which, in communication between the UE and the E-UTRAN,the UE performs CoMP communication with three cells as the CoMP activeset or CoMP measurement set, and changes a serving cell among thosecells.

This modification differs from the tenth embodiment in that in thismodification, the CoMP central entity performs MAC scheduling based ondata transmission/reception information (data parameters) of the servingcell, and thus, the scheduling information transmission link of StepsST10504 to ST10506 starts from the CoMP central entity and the CoMPcentral entity performs the CoMP set decision process when the servingcell is changed in Step ST10511.

In Steps ST10501 and ST10502, the links for transmitting MAC data unitsexist between the source cell and the target cell and between the sourcecell and the non-serving cell, similarly to Steps ST10401 and ST10403 ofthe tenth embodiment. In this modification, the MAC data units may alsobe transmitted via the central entity.

The scheduling information is notified as follows. In Steps ST10503 andST10545, the CoMP central entity performs scheduling based on thetransmission information notified from the MAC of the serving cell,using the transmission information transmission link. In Steps ST10504,ST10505, ST10506, ST10546, ST10547, and ST10548, scheduling results arenotified each cell using the scheduling information transmission links.

In the process of deciding a CoMP set when the serving cell is changed,for a CoMP set candidate proposed by the RRC of the target cell in theCoMP request in Step ST10510 of Step ST10509, in Step ST10511, the CoMPcentral entity decides a CoMP set in consideration of a trafficsituation of each cell. After that, in Steps ST10512, ST10513, andST10514, the information decided in Step ST10511 is notified as a CoMPresponse.

This modification differs from the tenth embodiment as described above,and thus, this modification allows the serving cell to be changed whileCoMP communication is continued, also in the case where there is a CoMPcentral entity.

The steps other than the steps described above, specifically, theprocesses of Steps ST10507, ST10508, and Steps ST10515 to ST10560 shownin FIGS. 67 to 70 are performed similarly to the processes of StepsST10405 and ST10406, and Steps ST10411 to 10454 in the tenth embodimentshown in FIGS. 63 to 66 described above.

Second Modification of Tenth Embodiment

A second modification of the tenth embodiment describes an example inthe case where the configuration of the tenth embodiment includes a cellunified entity composed of the RLC, PDCP, and RRC that manage threecells in common. In this modification, the RLCs and PDCPs of the cellsthat require data transmission between cells are aggregated in the cellunified entity, which simplifies each procedure compared with the tenthembodiment.

FIGS. 71 to 73 are diagrams showing an exemplary sequence of a mobilecommunication system in the second modification of the tenth embodiment.FIGS. 71 and 72 are continuous with each other at a boundary BL21. FIGS.72 and 73 are continuous with each other at a boundary BL22.

Similarly to the sequence shown in FIGS. 63 to 66 , this sequence showsan example in which in communication between the UE and the E-UTRAN, theUE performs CoMP communication with three cells as a CoMP active set orCoMP measurement set, and changes the serving cell among those cells.

Described here is an example in which communication is performed amongone cell unified entity composed of the RLC, PDCP, and RRC that managethree cells in common, one source sub cell composed of the PHY and MAC,one target sub cell, one non-serving sub cell, and one UE.

At the beginning of the sequence, first, the UE performs CoMPcommunication with three cells as a CoMP active set or CoMP measurementset. In this case, in Steps ST10601 to ST10605, the link fortransmitting an RLC data unit exists between the cell unified entity andthe source sub cell, the links for transmitting a MAC data unit and thelinks for notifying the scheduling information on the PDU scheduled bythe MAC of the source sub cell exist between the source sub cell and thetarget sub cell and between the source sub cell and the non-serving subcell. These links may be collectively referred to as a “MACPDU-relatedtransmission link”.

The link is described here as a logical one as in the tenth embodiment,an installation manner of which differing depending on actualinstallation. Also, not limited to the MACPDU-related transmission link,the communication paths for communication between sub cells and betweenthe sub cell and the cell unified entity include a logical link, asdescribed above.

In Step ST10606, it is judged that HO from the source cell to the targetcell is performed. In Step ST10607, the RRC of the cell unified entitydecides whether not to perform CoMP and decides a CoMP set at the targetcell, based on, for example, the CoMP cell information currentlyoperated in communication with the UE to become a target, the cellmeasurement information, the traffic situation of a CoMP candidate cell,and the CoMP cooperating set information.

In Step ST10608, the cell unified entity that has judged that HO isallowed and that CoMP is allowed transmits, to the UE, an RRC connectionreconfiguration message indicative of a change of the serving cellcontinuing CoMP.

Herein, as in the tenth embodiment, “RRC connection Reconfiguration”differs from “RRC connection Reconfiguration” described in documentssuch as Non-Patent Document 1, and explicitly shows that it is does notmean “Re-establishment” of, for example, RLC.

In Steps ST10609 and ST10610, the RRC of the cell unified entity alsoinstructs the PDCP and RLC to become targets to stop the process on theunprocessed data unit and stop downlink transmission to the MAC and RLC.

The PDCP and RLC of the cell unified entity that have been instructedstop the above-mentioned process. In Step ST10612, the RRC of the cellunified entity notifies the MAC that HO has been started. Also, the RLCof the cell unified entity performs the processes of Steps ST10613 andST10614.

The MAC that has been notified that HO had been started continues theprocess until forwarding of the currently-held data unit is completed.To judge a stop of the process, a timer may be provided to set a maximumprocess completion time. In this case, the process is stopped when theprocess is completed or the timer expires. The HARQ process (seeReference 9) needs to be taken into account in this case. The HARQprocess is an N process stop-and-wait system, which requires to set atimer value in consideration of the retransmission.

Also for uplink, the process of receiving data units from the UE iscontinued. To judge that the process is to be stopped, a timer differentfrom the above-mentioned timer is provided to stop the process after thecompletion of the MAC process by the UE. Similarly to downlink, the HARQprocess needs to be taken into account in the time until the timerexpires. For simpler installation, the same timer may be used in uplinkand downlink. If the HO completion by the UE described below isnotified, an instruction thereof may be used in judging to stopforwarding.

The UE that has received the RRC connection reconfiguration message inStep ST10608 stops the UL RLC and PDCP processes in Step ST10611,similarly to the cell.

Also as to the MAC, for uplink, the MAC continues the process untilforwarding of the currently-held data unit is completed, similarly tothe cell. To judge that the process is to be stopped, a timer isprovided, and in Step ST10615, the UE judges whether or not the MACprocess has been completed or the processing timer has expired, as inthe tenth embodiment.

Also for downlink, the process of receiving data units from the cell iscontinued. To judge that the process is to be stopped, a timer differentfrom the above-mentioned timer is provided to stop the process after thecompletion of the MAC process by the cell. Similarly to uplink, the HARQprocess needs to be taken into account in the time until the timerexpires. For simpler installation, the same timer may be used in uplinkand downlink.

If the MAC process has been completed or the processing timer hasexpired in Step ST10615, in Step ST10618, the UE transmits, to thetarget cell, an RRC connection reconfiguration complete messagecorresponding to the RRC connection reconfiguration. The UE performsprocedures for synchronization of Step ST10616 and TA notification ofStep ST10617 as required.

In Steps ST10620 and ST10621, the RRC of the cell unified entity thathas received the RRC connection reconfiguration complete messagenotifies the source sub cell and the non-serving sub cell that the UEhas completed a change of the serving cell.

The source sub cell, which has recognized in Step ST10620 that theserving cell had been changed from the notification that the UE hadcompleted HO, completes the MAC process of the UE to become a target.After the completion of the process, in Step ST10622, the source subcell notifies the cell unified entity of a MAC process complete message.

The non-serving cell, which has recognized in Step ST10621 that theserving cell had been changed from the notification that the UE hadcompleted HO, completes the MAC process of the UE to become a target.After the completion of the process, in Step ST10623, the non-servingcell notifies the cell unified entity of the MAC process completemessage

A series of processes of Step ST10619 is the procedure for strictlypreventing a process completion mismatch among the UE, the source subcell, and the cell unified entity, and therefore, needs not to beperformed for simplifying the processing procedure and speeding up achange of the serving cell.

In Step ST10625, the RRC of the cell unified entity that has transmittedan RRC connection reconfiguration message in Step ST10608 requests thetarget sub cell to establish an RLC transmission link with the cellunified entity and a MAC transmission link between cells included in theCoMP active set or CoMP measurement set.

In Steps ST10626 to ST10632, the target sub cell that has received theCoMP set request in Step ST10625 establishes the RLC transmission linkand the MAC transmission link in accordance with the instruction.

A series of processes of Step ST10624 may be performed during aninterval between the transmission of the RRC reconfiguration message inStep ST10608 and the transmission of the data request message in StepST10636. If the links cannot be established with the data unit link andthe scheduling information link between the MACs of the source sub cellside and the link of the target sub cell side in Steps ST10601 toST10605, as shown in FIGS. 71 to 73 , links may be established after thecompletion of HO.

In Steps ST10633, ST10634, and ST10635, the RRC of the cell unifiedentity that has received the RRC connection reconfiguration messagenotifies the MAC of the target sub cell and the RLC and PDCP of the cellunified entity that a change of the serving cell has been completed inthe UE HO complete message.

The MAC of the target sub cell that has received the UE HO completemessage in Step ST10633 checks whether the RLC transmission link and theMAC transmission link to become targets are established. If those linksare established, for uplink, the MAC of the target sub cell performs theprocess in accordance with the request from the UE and, for downlink,requests data from the RLC and performs the MAC process on the datatransmitted from the RLC. Communication with the cell in which the MACtransmission link is established is started together. If the RLCtransmission link and MAC transmission link to become targets are notestablished, the above-mentioned process is performed after these linksare established.

For uplink, the RLC of the cell unified entity that has received the UEHO complete message in Step ST10634 successively processes the uplinkRLC PDU transmitted from the MAC.

For downlink, when data transmission is requested in the data requestmessage of Step ST10636, in Step ST10637, the process and transmissionto the MAC are restarted. After that, the processes of Steps ST10638 andST10639 are performed.

For uplink, the PDCP of the cell unified entity that has received the UEHO complete message of Step ST10635 successively processes the uplinkPDCP PDU transmitted from the RLC.

For downlink, when data transmission is requested in the data requestmessage of Step ST10640, in Step ST10641, the PDCP PDU process andtransmission to the RLC are restarted.

As described above, in this modification, the introduction of the cellunified entity reduces the transmission between layers of the cells,allowing the serving cell to be changed more efficiently while keepingCoMP communication. Although this modification has described theconfiguration in which the cell unified entity is composed of the RLC,PDCP, and RRC, the cell unified entity may also include part of the MACor MAC. Alternatively, the RLC may be provided independently and thecell unified entity may be composed of only the RRC and PDCP. Althoughthe transmission amount between entities decreases as the cells areunified in a larger scale, the cell unified entity increases in size andcomplexity. Meanwhile, if the cells are unified in a smaller scale, thetransmission amount between entities increases but the cell unifiedentity decreases in size and complexity. This should be judged dependingon how the cell unified entity is used and installed. The presentinvention is appropriately applied through proper allocation ofinter-layer information transmission depending on the scale in whichcells are unified.

Eleventh Embodiment

In the case of performing the HO process on the UE being subjected toCoMP, the source cell needs to appropriately judge whether or not tostop CoMP and perform the HO process or to perform the HO process whileperforming CoMP. This embodiment will disclose the judgment method.

The HO process method is judged based on whether or not the target cellselected by the serving cell (source cell) is a cell in the CoMPmeasurement set for the UE to become a HO target. If the cell unifiedentity decides HO, the cell unified entity may judge the method of theHO process based on whether or not the target cell is a cell in the CoMPmeasurement set for the UE to become a HO target.

If the target cell is a cell in the CoMP measurement set for the UE tobecome a HO target, the serving cell judges to perform the HO processwhile performing CoMP on the UE. The method of the tenth embodiment maybe used as the method of performing the HO process while performingCoMP.

If the target cell is not the cell in the CoMP measurement set for theUE to become a HO target, the serving cell judges to stop performingCoMP on the UE and perform the HO process. The method of the eighthembodiment or the ninth embodiment may be used as the method of stoppingthe execution of CoMP and performing the HO process.

FIG. 74 is a diagram showing an exemplary sequence of a mobilecommunication system in an eleventh embodiment. FIG. 74 shows thesequence of judging to stop or continue CoMP in performing the HOprocess on the UE being subjected to CoMP.

The serving cell performs CoMP on the UE1 by the method disclosed inSteps ST1501 to ST1526 and ST1530 of FIGS. 15 and 16 .

In Step ST1526, the serving cell and the UE1 perform at least any one ofCoMP transmission/reception and CSI feedback.

In Step ST12101, the UE1 performs RRM measurement through CRSmeasurement. In Step ST12102, the UE1 reports, to the serving cell, theRRM measurement results in Step ST12101 as a measurement report message.The measurement in Step ST12101 includes CRS measurement of the servingcell itself. The measurement report in Step ST12102 may include the CRSmeasurement results of the serving cell itself.

In Step ST12103, the serving cell decides to perform the HO process onthe UE1 using the measurement report from the UE1. At this time, theserving cell decides a target cell.

In Step ST12104, the serving cell judges whether or not the target cellis a cell in the CoMP measurement set. The serving cell moves to StepST12105 if judging that the target cell is a cell in the CoMPmeasurement set in Step ST12104 or moves to Step ST12106 if judging thatthe target cell is not a cell in the CoMP measurement set in StepST12104.

In Step ST12105, the serving cell decides to perform the HO processwhile performing CoMP on the UE1 being a HO target.

In Step ST12106, the serving cell decides to stop performing CoMP on theUE1 and perform the HO process being a HO target.

If judging in Step ST12105 to perform the HO process while performingCoMP on the UE1 being a HO target, for example, the serving cell mayperform the HO process disclosed in the tenth embodiment. Meanwhile, ifjudging in Step ST12106 to stop performing CoMP on the UE1 and performthe HO process being a HO target, the serving cell may perform, forexample, the HO process disclosed in the eighth embodiment or the ninthembodiment.

If the target cell is a cell in the CoMP measurement set, the targetcell can also perform CoMP on the UE being a HO target, and thus, canperform the HO process while performing CoMP. This allows the targetcell to obtain a good communication quality.

If the target cell is not a cell in the CoMP measurement set, it has notbeen decided whether the target cell can perform CoMP on the UE being aHO target. Therefore, when CoMP is stopped and the HO process isperformed, a radio link can be connected more reliably at the targetcell.

The HO process method is judged based on whether or not the target cellis an in-CoMP-measurement-set cell, as described above, so that the HOprocess suitable for the state of the UE to become a HO target can beperformed. This improves a throughput as the mobile communicationsystem.

First Modification of Eleventh Embodiment

This modification will disclose another method of judging to stop CoMPand perform the HO process or to perform the HO process while performingCoMP when the HO process is performed on the UE being subjected to CoMP.

In this modification, the HO process method is judged based on whetheror not the target cell selected by the serving cell is a cell in theCoMP active set for the UE to become a HO target.

If the target cell is a cell in the CoMP active set for the UE to becomea HO target, the serving cell judges to perform the HO process whileperforming CoMP on the UE. The method of the tenth embodiment may beused as the method of performing the HO process while performing CoMP.

If the target cell is not a cell in the CoMP active set for the UE tobecome a HO target, the serving cell judges to stop performing CoMP onthe UE and perform the HO process. The method of the eighth embodimentor the ninth embodiment may be used as the method of stopping theexecution of CoMP and performing the HO process.

The sequence in this modification may be obtained by partly changing thesequence shown in FIG. 74 . In Step ST12104 of FIG. 74 , the servingcell may judge whether or not the target cell is a cell in the CoMPactive set.

If the target cell is a cell in the CoMP active set, the target cell canalso perform CoMP on the UE being a HO target, and thus, can perform theHO process while performing CoMP. This also allows the target cell toobtain a good communication quality.

If the target cell is not a cell in the CoMP active set, it has yet tobe decided whether the target cell can perform CoMP on the UE being a HOtarget. Therefore, when CoMP is stopped and the HO process is performed,a radio link can be connected more reliably at the target cell.

As described above, the HO process method is judged based on whether ornot the target cell is an in-CoMP-active-set cell, so that the HOprocess suitable for the state of the UE to become a HO target can beperformed. This improves a throughput as the mobile communicationsystem.

Second Modification of Eleventh Embodiment

This modification will disclose another method of judging to stop CoMPand perform the HO process or to perform the HO process while performingCoMP when performing the HO process on the UE being subjected to CoMP.

In this modification, the HO process method is judged based on which RSmeasurement results by the UE to become a HO target are used when theserving cell selects a target cell.

If the target cell is selected using the CSI-RS measurement results bythe UE to become a HO target, the serving cell judges to perform the HOprocess while performing CoMP on the UE. The method of the tenthembodiment may be used as the method of performing the HO process whileperforming CoMP.

If the target cell is selected using the CRS measurement results by theUE to become a HO target, the serving cell judges to stop performingCoMP on the UE and perform the HO process. The method of the eighthembodiment or the ninth embodiment may be used as the method of stoppingthe execution of CoMP and performing the HO process.

The sequence in this modification may be obtained by partly changing thesequence shown in FIG. 74 . In Step ST12104 of FIG. 74 , the servingcell may judge whether or not the target cell is selected using theCSI-RS measurement results by the UE to become a HO target or isselected using the CRS measurement results. The serving cell may move toStep ST12105 if using the CSI-RS measurement results or move to StepST12106 if using the CRS measurement results.

If the target cell is selected using the CSI-RS measurement results, thetarget cell can obtain a good communication quality even when performingCoMP on the UE being a HO target, and thus, may perform the HO processwhile performing CoMP.

If the target cell is selected using the CRS measurement results, it isunclear whether or not the target cell can obtain a good communicationquality when performing CoMP on the UE being a HO target. Therefore, aradio link can be more reliably connected at the target cell by stoppingCoMP and performing the HO process.

As described above, the HO process method is judged based on whether thetarget cell is selected by measuring the CSI-RS or the target cell isselected by measuring the CRS, so that the HO process suitable for thestate of the UE to become a HO target can be performed. This improves athroughput as the mobile communication system.

Third Modification of Eleventh Embodiment

This modification will disclose another method of judging, in performingthe HO process on the UE being subjected to CoMP, to stop CoMP andperform the HO process or to perform the HO process while performingCoMP.

In this modification, the HO process method is judged using the numberof CoMP transmission points for the UE to become a HO target. For thisjudgment, a threshold is provided for the number of CoMP transmissionpoints.

If the number of CoMP transmission points for the UE to become a HOtarget is not larger than the threshold, the serving cell performs theHO process while performing CoMP on the UE. The method of the tenthembodiment may be used as the method of performing the HO process whileperforming CoMP.

If the number of CoMP transmission points for the UE to become a HOtarget is larger than the threshold, the serving cell judges to stopperforming CoMP on the UE and perform the HO process. The method of theeighth embodiment or the ninth embodiment may be used as the method ofstopping the execution of CoMP and performing the HO process.

The sequence in this modification may be obtained by partly changing thesequence shown in FIG. 74 . In Step ST12104 of FIG. 74 , the servingcell may judge whether or not the number of CoMP transmission points forthe UE to become a HO target is not larger than the predeterminedthreshold.

If the number of CoMP transmission points is larger than thepredetermined threshold, the control of the network becomes complicatedif the HO process is performed while performing CoMP. This is because atleast any one of the data unit and scheduling information forcoordinated control needs to be transmitted between a large number ofCoMP transmission points. Therefore, if the number of CoMP transmissionpoints is larger than the predetermined threshold, when CoMP is stoppedand the HO process is performed, the processing load of a network can bereduced more and a radio link can be connected more reliably at thetarget cell.

As described above, the HO process method is judged using the number ofCoMP transmission points, so that the HO process suitable for the stateof the UE to become a HO target can be performed. This improves athroughput as the mobile communication system.

Fourth Modification of Eleventh Embodiment

This modification will disclose another method of judging the HO processmethod using the number of CoMP transmission points for the UE to becomea HO target. A threshold is provided for the number of CoMP transmissionpoints to judge using the number of CoMP transmission points.

If the number of CoMP transmission points for the UE to become a HOtarget is not less than the threshold, the serving cell performs the HOprocess while performing CoMP on the UE. The method of the tenthembodiment may be used as the method of performing the HO process whileperforming CoMP.

If the number of CoMP transmission points for the UE to become a HOtarget is smaller than the threshold, the serving cell judges to stopperforming CoMP on the UE and perform the HO process. The method of theeighth embodiment or the ninth embodiment may be used as the method ofstopping the execution of CoMP and performing the HO process.

The sequence in this modification may be obtained by partly changing thesequence shown in FIG. 74 . In Step ST12104 of FIG. 74 , the servingcell may judge whether or not the number of CoMP transmission points forthe UE to become a HO target is not less than the predeterminedthreshold.

If the number of CoMP transmission points is smaller than thepredetermined threshold, the communication quality necessary for acommunication link with one cell is likely to be obtained. Therefore,the control load of a network can be reduced by stopping CoMP andperforming the HO process than by performing the HO process whileperforming CoMP.

If the number of CoMP transmission points is not less than thepredetermined threshold, the required communication quality is unlikelyto be obtained unless the data transmission/reception to/from aplurality of cells is used. Thus, a better communication quality can beobtained by performing the HO process while performing CoMP. The HOprocess method is judged using the number of CoMP transmission points,so that the HO process suitable for the state of the UE to become a HOtarget can be performed. This improves a throughput as the mobilecommunication system.

Fifth Modification of Eleventh Embodiment

This modification will disclose another method of judging, when the HOprocess is performed on the UE being subjected to CoMP, to stop CoMP andperform the HO process or to perform the HO process while performingCoMP.

In this modification, the HO process method is judged using the mobilityspeed of the UE to become a HO target. For this judgment, a threshold isprovided for the mobility speed of the UE.

If the mobility speed of the UE to become a HO target is not larger thanthe threshold, the serving cell judges to perform the HO process whileperforming CoMP on the UE. The method of the tenth embodiment may beused as the method of performing the HO process while performing CoMP.

If the mobility speed of the UE to become a HO target is larger than thethreshold, the serving cell judges to stop performing CoMP on the UE andperform the HO process. The method of the eighth embodiment or the ninthembodiment may be used as the method of stopping the execution of CoMPand performing the HO process.

The sequence in this modification may be obtained by partly changing thesequence shown in FIG. 74 . In Step ST12104 of FIG. 74 , the servingcell may judge whether or not the mobility speed of the UE to become aHO target is not larger than the predetermined threshold.

If the mobility speed of the UE being a HO target is larger than thepredetermined threshold, control of the network for performing the HOprocess while performing CoMP is more affected by a transmission delayof at least any one of the data unit and the scheduling information forcoordinated control. If the mobility speed of the UE being a HO targetis larger than the predetermined threshold, the UE is likely to beoutside the covarage of a new serving cell in a short time, increasing apossibility that the execution of CoMP will fail. Or, even if CoMP doesnot fail, a cell for optimum CoMP cannot be selected, reducing effectsof CoMP. Therefore, if the mobility speed of the UE being a HO target islarger than the predetermined threshold, by stopping CoMP and performingthe HO process, a radio link at the target cell can be more reliablyconnected.

As described above, the HO process method is judged using the mobilityspeed of the UE being a HO target, so that the HO process suitable forthe state of the UE to become a HO target can be performed. Thisimproves a throughput as the mobile communication system.

The following three (1) to (3) will be disclosed as indicators for themobility speed of the UE.

(1) Actual speed. The UE may measure speed using GPS or the like. Themeasurement results may be notified the serving cell regularly orperiodically from the UE. Or, the measurement results may be notifiedwith a measurement report. This allows the serving cell to use themobility speed information of the UE.

(2) Mobility speed information included in positioning information ofUE. The method of obtaining the location information of the UE,disclosed in the third embodiment, may be used as the method in whichthe serving cell obtains the mobility speed information.

(3) Mobility speed information obtained from the number of cellreselections. Specifically, the mobility speed information is a speedscaling factor. In the LTE, the serving cell obtains the mobility speedinformation and thus can use that information.

Sixth Modification of Eleventh Embodiment

This modification will disclose another method of judging, in the caseof performing the HO process on the UE being subjected to CoMP, to stopCoMP and perform the HO process or to perform the HO process whileperforming CoMP.

In this modification, the HO process method is judged using thecommunication quality with the serving cell. Specifically, the HOprocess method is judged using the communication quality with the sourcecell in HO. For this judgment, a threshold is provided for thecommunication quality.

If the communication quality between the UE to become a HO target andthe serving cell is not larger than the threshold, the serving celljudges to perform the HO process while performing CoMP on the UE. Themethod of the tenth embodiment may be used as the method of performingthe HO process while performing CoMP.

If the communication quality between the UE to become a HO target andthe serving cell is larger than the threshold, the serving cell judgesto stop performing CoMP on the UE and perform the HO process. The methodof the eighth embodiment or the ninth embodiment may be used as themethod of stopping the execution of CoMP and performing the HO process.

The sequence in this modification may be obtained by partly changing thesequence shown in FIG. 74 . In Step ST12104 of FIG. 74 , the servingcell may judge whether or not the communication quality between the UEto become a HO target and the serving cell is not larger than thepredetermined threshold.

If the communication quality between the UE to become a HO target andthe serving cell is larger than the predetermined threshold, thecommunication quality necessary for the communication link with one cellis likely to be obtained. Therefore, the control load of a network canbe reduced by stopping CoMP and performing the HO process than byperforming the HO process while performing CoMP.

Meanwhile, if the communication quality between the UE to become a HOtarget and the serving cell is not larger than the predeterminedthreshold, the required communication quality is unlikely be obtainedunless the data transmission/reception to/from a plurality of cell isused. A better communication quality can be obtained by performing theHO process while performing CoMP.

As described above, the HO process method is judged using thecommunication quality with the serving cell, so that the HO processsuitable for the state of the UE to become a HO target can be performed.This improves a throughput as the mobile communication system.

Seventh Modification of Eleventh Embodiment

This modification will disclose another method of judging, in the caseof performing the HO process on the UE being subjected to CoMP, to stopCoMP and perform the HO process or to perform the HO process whileperforming CoMP.

In this modification, the HO process method is judged using thecommunication quality with a new serving cell. Specifically, the HOprocess method is judged using the communication quality with the targetcell in HO. For this judgment, a threshold is provided for thecommunication quality.

If the communication quality between the UE to become a HO target andthe target cell is not larger than the threshold, the serving celljudges to perform the HO process while performing CoMP on the UE. Themethod of the tenth embodiment may be used as the method of performingthe HO process while performing CoMP.

If the communication quality between the UE to become a HO target andthe target cell is larger than the threshold, the serving cell judges tostop performing CoMP on the UE and perform the HO process. The method ofthe eighth embodiment or the ninth embodiment may be used as the methodof stopping the execution of CoMP and performing the HO process. Themeasurement report by the UE may be used for the communication qualitybetween the UE to become a HO target and the target cell. Themeasurement report may be used for CoMP, for mobility, or for both ofthem. The communication quality between the UE to become a HO target andthe target cell is notified the serving cell. The measurement by the UEmay be the CRS measurement results or the CSI-RS measurement results.

The sequence in this modification may be obtained by partly changing thesequence shown in FIG. 74 . In Step ST12104 of FIG. 74 , the servingcell may judge whether or not the communication quality between the UEto become a HO target and the target cell is not larger than thepredetermined threshold.

If the communication quality between the UE to become a HO target andthe target cell is larger than the predetermined threshold, thecommunication quality necessary for a communication link with one cellis likely to be obtained. Therefore, the control load of a network canbe reduced more by stopping CoMP and performing the HO process than byperforming the HO process while performing CoMP.

Meanwhile, if the communication quality between the UE to become a HOtarget and the target cell is not larger than the predeterminedthreshold, the required communication quality cannot be obtained unlessdata transmission/reception to/from a plurality of cells is used.Therefore, a better communication quality can be obtained by performingthe HO process while performing CoMP.

As described above, the HO process method is judged using thecommunication quality with the target cell, so that the HO processsuitable for the state of the UE to become a HO target can be performed.This improves a throughput as the mobile communication system.

Eighth Modification of Eleventh Embodiment

This modification will disclose another method of judging, in the caseof performing the HO process on the UE being subjected to CoMP, to stopCoMP and perform the HO process or to perform the HO process whileperforming CoMP.

In this modification, the HO process method is judged using the types ofthe service during communication. If the type of service duringcommunication with the UE to become a HO target is a certain type, theserving cell judges to perform the HO process while performing CoMP onthe UE. The method of the tenth embodiment may be used as the method ofperforming the HO process while performing CoMP.

If the type of service during communication with the UE to become a HOtarget is not a certain type, the serving cell judges to stop performingCoMP on the UE and perform the HO process. The method of the eighthembodiment or the ninth embodiment may be used as the method of stoppingthe execution of CoMP and performing the HO process.

The sequence in this modification may be obtained by partly changing thesequence shown in FIG. 74 . In Step ST12104 of FIG. 74 , the servingcell may judge whether or not the type of service during communicationwith the UE to become a HO target is a certain type.

As described above, the HO process method is judged using the type ofservice during communication, so that the HO process suitable forservice during communication can be performed.

Ninth Modification of Eleventh Embodiment

This modification will disclose another method of judging, in the caseof performing the HO process on the UE being subjected to CoMP, to stopCoMP and perform the HO process or to perform the HO process whileperforming CoMP.

In this modification, the HO process method is judged using a delay timerequired for service during communication. For this judgment, athreshold is provided for the delay time required for service.

If the delay time required for service during communication with the UEto become a HO target is not larger than the threshold, the serving celljudges to perform the HO process while performing CoMP on the UE. Themethod of the tenth embodiment may be used as the method of performingthe HO process while performing CoMP.

If the delay time required for service during communication with the UEto become a HO target is larger than the threshold, the serving celljudges to stop performing CoMP on the UE and perform the HO process. Themethod of the eighth embodiment or the ninth embodiment may be used asthe method of stopping the execution of CoMP and performing the HOprocess.

The sequence in this modification may be obtained by partly changing thesequence shown in FIG. 74 . In Step ST12104 of FIG. 74 , the servingcell may judge whether or not the delay time required for service duringcommunication with the UE to become a HO target is not larger than thepredetermined threshold.

If the delay time required for service during communication with the UEto become a HO target is not larger than the predetermined threshold, agood communication quality is required for reducing the delay time dueto, for example, the retransmission process as much as possible. Abetter communication quality can be obtained by performing the HOprocess while keeping CoMP than by stopping CoMP and performing the HOprocess, further reducing a delay time. The HO process method is judgedusing the delay time required for service during communication, allowingfor the HO process suitable for service during communication. Thisimproves a throughput as the mobile communication system.

Although this modification has disclosed to judge the HO process methodusing a delay time required for service during communication, not thedelay time but the judgment indicators disclosed in (1) to (5) below maybe used.

(1) Error rate required for service during communication (packet errorloss rate).

Resource type required for service during communication. Examples of theresource types include a guaranteed bit rate (GBR) and Non-GBR.

Priority for service during communication.

Quality of service (QoS) of service during communication.

QoS class identifier (QCI) of service during communication.

As described in (1) above, the HO process method is judged using anerror rate required for service during communication. For this judgment,a threshold is provided for the error rate required for service.

If the error rate required for service during communication with the UEto become a HO target is not larger than the threshold, the serving celljudges to perform the HO process while performing CoMP on the UE. Themethod of the tenth embodiment may be applied as the method ofperforming the HO process while performing CoMP.

If the error rate required for service during communication with the UEto become a HO target is larger than the threshold, the serving celljudges to stop performing CoMP on the UE and perform the HO process. Themethod of the eighth embodiment or the ninth embodiment may be appliedas the method of stopping the execution of CoMP and performing the HOprocess.

The sequence in the case of using the judgment indicator (1) above maybe obtained by partly changing the sequence shown in FIG. 74 . In StepST12104 of FIG. 74 , the serving cell may judge whether or not the errorrate required for service during communication with the UE to become aHO target is not larger than the predetermined threshold. This allowsfor the HO process suitable for service during communication, improvinga throughput as the mobile communication system.

The HO process method is judged using the resource type required forservice during communication, as described in (2) above. If the resourcetype required for service during communication with the UE to become aHO target is the GBR, the serving cell judges to perform the HO processwhile performing CoMP on the UE. The method of the tenth embodiment maybe applied as the method of performing the HO process while performingCoMP.

If the resource type required for service during communication with theUE to become a HO target is not the GBR, the serving cell judges to stopperforming CoMP on the UE and perform the HO process. The method of theeighth embodiment or the ninth embodiment may be applied as the methodof stopping the execution of CoMP and performing the HO process.

The sequence in the case of using the judgment indicator (2) above maybe obtained by partly changing the sequence shown in FIG. 74 . In StepST12104 of FIG. 74 , the serving cell may judge whether or not theresource type required for service during communication with the UE tobecome a HO target is the GBR. This allows for the HO process suitablefor service during communication, improving a throughput as the mobilecommunication system.

The HO process method is judged using the service priority duringcommunication, as described in (3) above. For this judgment, a thresholdis provided for the service priority.

If the service priority during communication with the UE to become a HOtarget is not less than the threshold, the serving cell judges toperform the HO process while performing CoMP on the UE. The method ofthe tenth embodiment may be applied as the method of performing the HOprocess while performing CoMP.

If the service priority during communication with the UE to become a HOtarget is smaller than the threshold, the serving cell judges to stopperforming CoMP on the UE and perform the HO process. The method of theeighth embodiment or the ninth embodiment may be applied as the methodof stopping the execution of CoMP and performing the HO process.

The sequence in the case of using the judgment indicator (3) above maybe obtained by partly changing the sequence shown in FIG. 74 . In StepST12104 of FIG. 74 , the serving cell may judge whether or not theservice priority during communication with the UE to become a HO targetis not less than the threshold. This allows for the HO process suitablefor service during communication, improving a throughput as the mobilecommunication system.

The HO process method is judged using the QoS of service duringcommunication, as described in (4) above. For this judgment, the QoSsare categorized so that categories are numbered. For example, categoriesare numbered in ascending order from a category with a good QoS, and athreshold is provided for the numbers.

If the category number of the QoS of service during communication withthe UE to become a HO target is not larger than the threshold, theserving cell judges to perform the HO process while performing CoMP onthe UE. The method of the tenth embodiment may be applied as the methodof performing the HO process while performing CoMP.

If the category number of the QoS of service during communication withthe UE to become a HO target is larger than the threshold, the servingcell judges to stop performing CoMP on the UE and perform the HOprocess. The method of the eighth embodiment or the ninth embodiment maybe applied as the method of stopping the execution of CoMP andperforming the HO process.

The sequence in the case of using the judgment indicator (4) above maybe obtained by party changing the sequence shown in FIG. 74 . In StepST12104 of FIG. 74 , the serving cell may judge whether or not thecategory number of the QoS of service during communication with the UEto become a HO target is not larger than the threshold. This allows forthe HO process suitable for service during communication, improving athroughput as the mobile communication system.

As described in (5), the HO process method is judged using the QCI ofservice during communication. As disclosed in TS23.203 V11.2.0(hereinafter, referred to “Reference 10”) by 3GPP, the QCI refers to anindicator when a plurality of demand indicators for service areclassified. For judgment using the QCI, a threshold is provided for theQCI.

If the QCI of service during communication with the UE to become a HOtarget is not larger than the threshold, the serving cell judges toperform the HO process while performing CoMP on the UE. The method ofthe tenth embodiment may be applied as the method of performing the HOprocess while performing CoMP.

If the QCI of service during communication with the UE to become a HOtarget is larger than the threshold, the serving cell judges to stopperforming CoMP on the UE and perform the HO process. The method of theeighth embodiment or the ninth embodiment may be applied as the methodof stopping the execution of CoMP and performing the HO process.

The sequence in the case of using the judgment indicator (5) above maybe obtained by partly changing the sequence shown in FIG. 74 . In StepST12104 of FIG. 74 , the serving cell may judge whether or not the QCIof service during communication with the UE to become a HO target is notlarger than the threshold. This allows for the HO process suitable forservice during communication, improving a throughput as the mobilecommunication system.

Tenth Modification of Eleventh Embodiment

This modification will disclose another method of judging, when the HOprocess is performed on the UE being subjected to CoMP, to stop CoMP andperform the HO process or to perform the HO process while performingCoMP.

In this modification, the HO process method is judged based on whetheror not the target cell selected by the serving cell is a cell in theCoMP cooperating set to which the serving cell belongs.

The serving cell judges to perform the HO process between the cells inthe CoMP cooperating set while performing CoMP on the UE if the targetcell is a cell in the CoMP cooperating set to which its own cellbelongs. The method of the first modification of the tenth embodimentmay be applied as the method of performing the HO process whileperforming CoMP between the cells in the CoMP cooperating set.

The serving cell judges to perform the HO process with the cell outsidethe CoMP cooperating set while performing CoMP on the UE if the targetcell is not a cell in the CoMP cooperating set to which its own cellbelongs. The method of the tenth embodiment may be applied as the methodof performing the HO process while performing CoMP with the cell outsidethe CoMP cooperating set.

FIG. 75 is a diagram showing an example of the sequence of a mobilecommunication system of the tenth modification of the eleventhembodiment. The sequence shown in FIG. 75 is similar to the sequenceshown in FIG. 74 , and thus, the same steps will be denoted by the samestep numbers and common description will be omitted.

In this modification, in Step ST12201 of FIG. 75 , the serving cell mayjudge whether or not the target cell is a cell in the CoMP cooperatingset to which the serving cell belongs.

If the target cell is a cell in the CoMP cooperating set to which theserving cell belongs, in Step ST12105, the serving cell judges toperform the HO process between cells in the CoMP cooperating set whileperforming CoMP. In this case, the HO process disclosed in the firstmodification of the tenth embodiment may be performed.

If the target cell is not a cell in the CoMP cooperating set to whichthe serving cell belongs, in Step ST12106, the serving cell judges toperform the HO process with a cell outside the CoMP cooperating setwhile performing CoMP. In this case, the HO process disclosed in thetenth embodiment may be performed.

The HO process can be thus performed while performing CoMP on the UEbeing a HO target, depending on whether or not the target cell is a cellin the CoMP cooperating set to which its own cell belongs. Therefore,the target cell can obtain a good communication quality as well. Thisimproves a throughput as the mobile communication system.

The following three (1) to (3) will be disclosed as the method in whichthe serving cell recognizes whether or not the target cell is a cell inthe CoMP cooperating set.

(1) The serving cell inquires, from the central entity, whether or notthe target cell belongs to the CoMP cooperating set of its own cell.

The central entity is an entity that intensively adjusts one or aplurality of points, and accordingly, is caused to recognize the cellsin the CoMP cooperating set.

In Step ST12103, the serving cell selects a target cell and notifies thecentral entity of a message for inquiring whether or not the selectedtarget cell is a cell in the CoMP cooperating set of its own cell. Themessage may include the cell identity of the target cell. This allowsthe central entity to specify the target cell. Or, the message mayinclude the cell identity of the serving cell. This allows the centralentity to specify the serving cell being a demand source.

The central entity notifies the serving cell being a demand source ofwhether or not the target cell is a cell in the CoMP cooperating set towhich the serving cell being a demand source belongs. This allows theserving cell to recognize whether or not the target cell is a cell inthe CoMP cooperating set of its own cell.

The serving cell may recognize whether or not the target cell is a cellin the CoMP cooperating set of its own cell, and then, reselect thetarget cell. This allows for the selection whether HO in the CoMPcooperating set is performed or HO between CoMP cooperating sets isperformed. Therefore, the HO process suitable for the state of the UE tobecome a HO target can be performed, improving a throughput as themobile communication system.

The method (1) above is not limited for the target cell alone but may beapplied as the method of recognizing whether or not a desired cell is acell in the CoMP cooperating set.

Although the entity that recognizes cells included in the CoMPcooperating set is the central entity herein, not limited thereto, aninquiry may be made to the entity, node, or device that recognizes thecells included in the CoMP cooperating set. For example, if the nodethat recognizes the cells included in the CoMP cooperating set is anoperation administration and maintenance (OAM), an inquiry may be madeto the OAM. Or, if the entity that recognizes the cells included in theCoMP cooperating set is the cell unified entity, an inquiry may be madeto the cell unified entity. The same holds true for the cases in whichthe entity and node that recognize the cells included in the CoMPcooperating set are not the cell unified entity and OAM but are the MME,eNB, and HeNB-GW.

(2) The serving cell inquires the CoMP cooperating set of the targetcell from the target cell.

After selecting the target cell in Step ST12103, the serving cellnotifies the selected target cell of the message for inquiring about theCoMP cooperating set of the target cell. The serving cell may notify thetarget cell via the MME. At this time, the cell identity of the servingcell may be notified. This allows the target cell to recognize theserving cell being a demand source.

An identifier may be provided for the CoMP cooperating set. Thisidentifier can be used as the method for identifying the CoMPcooperating set, not limited to this modification. Each cell mayrecognize to which CoMP cooperating set its own cell belongs. Forexample, the central entity may preliminarily notify each cell of towhich CoMP cooperating set its own cell belongs.

The target cell that has received the notification of the message forinquiring the CoMP cooperating set of the target cell notifies theserving cell of the identifier of the CoMP cooperating set to which itsown cell belongs. The target cell may notify the serving cell via theMME. This allows the serving cell to recognize whether or not the targetcell is a cell in the CoMP cooperating set of its own cell. The servingcell may recognize whether or not the target cell is a cell in the CoMPcooperating set of its own cell, and then, reselect the target cell.

(3) The serving cell inquires, from the target cell, whether or not thetarget cell belongs to the CoMP cooperating set of its own cell.

After selecting a target cell in Step ST12103, the serving cell notifiesthe selected target cell of the CoMP cooperating set of its own cell.Specifically, the serving cell may notify the identifier of the CoMPcooperating set of its own cell. The serving cell may notify the targetcell via the MME. At this time, the cell identify of the serving cellmay also be notified. This allows the target cell to recognize theserving cell being an inquiry source.

The target cell that has received the notification of the CoMPcooperating set of its own cell judges whether or not it belongs to theset from the identifier of the CoMP cooperating set of the serving cell.The target cell notifies the serving cell being a demand source of thejudgment results. This allows the serving cell to recognize whether ornot the target cell is a cell in the CoMP cooperating set of its owncell. The serving cell may recognize whether or not the target cell is acell in the CoMP cooperating set of its own cell and then reselect thetarget cell.

The methods (2) and (3) above may use a HO request message and a HOrequest response message to be notified from the source cell, here, theserving cell to the target cell when the HO process is performed.

The method described above allows the serving cell to recognize whetheror not the target cell is a cell in the CoMP cooperating set.

This embodiment and the modifications thereof may be appropriatelyapplied in combination. The embodiment and the modifications thereof arealso applicable to the judgment whether or not to perform CoMP on theUE.

The methods disclosed in the present invention can be appropriatelyperformed in combination. This allows for control corresponding to thesystem condition.

Although the embodiments have described CoMP in the LTE-A, the techniqueregarding the coordinated multiple point transmission and receptiondisclosed in the present invention can be appropriately used in othermobile communication system or a heterogeneous communication system.

While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous modifications andvariations can be devised without departing from the scope of theinvention.

DESCRIPTION OF REFERENCE NUMERALS

1401 RRM measurement set, 1402 CoMP measurement set, 1403 CoMPtransmission point, 1601 CoMP active set.

1. (canceled)
 2. A mobile communication system including a plurality ofbase stations and a user equipment, the plurality of base stationsperforming radio communication with the user equipment in a coordinatedmanner with each other, wherein a base station among the plurality ofbase stations transmits measurement object information to the userequipment, the measurement object information indicating a signal to bemeasured by the user equipment among signals transmitted from theplurality of base stations, the user equipment transmits measurementresult information to the base station, the measurement resultinformation indicating a measurement result of a measurement objectsignal indicated by the measurement object information, and whenhandover is performed, the base station transmits a signal notifyingthat the measurement object signal is released from a measurement objectto the user equipment.
 3. The mobile communication system according toclaim 2, wherein the measurement object signal is a reference signal tobe measured by the user equipment for obtaining a state of a channel. 4.The mobile communication system according to claim 2, wherein themeasurement object information is transmitted using a communicationsignal dedicatedly provided for the user equipment.
 5. The mobilecommunication system according to claim 2, wherein the measurementobject information is transmitted using a radio resource control (RRC)signal.
 6. The mobile communication system according to claim 2, whereinthe measurement result information is transmitted from the userequipment to the base station that transmits the measurement objectinformation periodically.
 7. A base station including a controller, thebase station performing radio communication with a user equipment in acoordinated manner with another base station, wherein the controllerperforms control so that: measurement object information is transmittedto the user equipment, the measurement object information indicating asignal to be measured by the user equipment among signals transmittedfrom the base station and the other base station; measurement resultinformation is received from the user equipment, the measurement resultinformation indicating a measurement result of a measurement objectsignal indicated by the measurement object information; and whenhandover is performed, a signal notifying that the measurement objectsignal is released from a measurement object is transmitted to the userequipment.
 8. A user equipment including a controller, the userequipment performing radio communication with a plurality of basestations that operate in a coordinated manner with each other, whereinthe controller performs control so that: measurement object informationis received from a base station among the plurality of base stations,the measurement object information indicating a signal to be measured bythe user equipment among signals transmitted from the plurality of basestations; measurement result information is transmitted to the basestation, the measurement result information indicating a measurementresult of a measurement object signal indicated by the measurementobject information; and when handover is performed, a signal notifyingthat the measurement object signal is released from a measurement objectis received from the base station.